Wireless communication method and wireless communication terminal in high-density environment including overlapped basic service set

ABSTRACT

Provided is a wireless communication terminal. The wireless communication terminal includes a transceiver; and a processor. The processor is configured to receive a signaling field of a first PLCP Protocol Data Unit (PPDU) through the transceiver, and access a channel based on information identifying a Basic Service Set (BSS) indicated by the signaling field.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/KR2016/011854 filed on Oct. 20, 2016, which claims the priorityto Korean Patent Application No. 10-2015-0146203 filed in the KoreanIntellectual Property Office on Oct. 20, 2015, Korean Patent ApplicationNo. 10-2015-0150311 filed in the Korean Intellectual Property Office onOct. 28, 2015, Korean Patent Application No. 10-2015-0154100 filed inthe Korean Intellectual Property Office on Nov. 3, 2015, Korean PatentApplication No. 10-2016-0029975 filed in the Korean IntellectualProperty Office on Mar. 12, 2016, Korean Patent Application No.10-2016-0044465 filed in the Korean Intellectual Property Office on Apr.11, 2016, and Korean Patent Application No. 10-2016-0062425 filed in theKorean Intellectual Property Office on May 20, 2016, the entire contentsof which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a wireless communication method and awireless communication terminal in a high-density environment includingan overlapped basic service set.

BACKGROUND ART

In recent years, with supply expansion of mobile apparatuses, a wirelesscommunication technology that can provide a rapid wireless Internetservice to the mobile apparatuses has been significantly spotlighted.The wireless communication technology allows mobile apparatusesincluding a smart phone, a smart pad, a laptop computer, a portablemultimedia player, an embedded apparatus, and the like to wirelesslyaccess the Internet in home or a company or a specific service providingarea.

One of most famous wireless communication technology is wireless LANtechnology. Institute of Electrical and Electronics Engineers (IEEE)802.11 has commercialized or developed various technological standardssince an initial wireless LAN technology is supported using frequenciesof 2.4 GHz. First, the IEEE 802.11b supports a communication speed of amaximum of 11 Mbps while using frequencies of a 2.4 GHz band. IEEE802.11a which is commercialized after the IEEE 802.11b uses frequenciesof not the 2.4 GHz band but a 5 GHz band to reduce an influence byinterference as compared with the frequencies of the 2.4 GHz band whichare significantly congested and improves the communication speed up to amaximum of 54 Mbps by using an Orthogonal Frequency DivisionMultiplexing (OFDM) technology. However, the IEEE 802.11a has adisadvantage in that a communication distance is shorter than the IEEE802.11b. In addition, IEEE 802.11g uses the frequencies of the 2.4 GHzband similarly to the IEEE 802.11b to implement the communication speedof a maximum of 54 Mbps and satisfies backward compatibility tosignificantly come into the spotlight and further, is superior to theIEEE 802.11a in terms of the communication distance.

Moreover, as a technology standard established to overcome a limitationof the communication speed which is pointed out as a weak point in awireless LAN, IEEE 802.11n has been provided. The IEEE 802.11n aims atincreasing the speed and reliability of a network and extending anoperating distance of a wireless network. In more detail, the IEEE802.11n supports a high throughput (HT) in which a data processing speedis a maximum of 540 Mbps or more and further, is based on a multipleinputs and multiple outputs (MIMO) technology in which multiple antennasare used at both sides of a transmitting unit and a receiving unit inorder to minimize a transmission error and optimize a data speed.Further, the standard can use a coding scheme that transmits multiplecopies which overlap with each other in order to increase datareliability.

As the supply of the wireless LAN is activated and further, applicationsusing the wireless LAN are diversified, the need for new wireless LANsystems for supporting a higher throughput (very high throughput (VHT))than the data processing speed supported by the IEEE 802.11n has comeinto the spotlight. Among them, IEEE 802.11ac supports a wide bandwidth(80 to 160 MHz) in the 5 GHz frequencies. The IEEE 802.11ac standard isdefined only in the 5 GHz band, but initial 11ac chipsets will supporteven operations in the 2.4 GHz band for the backward compatibility withthe existing 2.4 GHz band products. Theoretically, according to thestandard, wireless LAN speeds of multiple stations are enabled up to aminimum of 1 Gbps and a maximum single link speed is enabled up to aminimum of 500 Mbps. This is achieved by extending concepts of awireless interface accepted by 802.11n, such as a wider wirelessfrequency bandwidth (a maximum of 160 MHz), more MIMO spatial streams (amaximum of 8), multi-user MIMO, and high-density modulation (a maximumof 256 QAM). Further, as a scheme that transmits data by using a 60 GHzband instead of the existing 2.4 GHz/5 GHz, IEEE 802.11ad has beenprovided. The IEEE 802.11ad is a transmission standard that provides aspeed of a maximum of 7 Gbps by using a beamforming technology and issuitable for high bit rate moving picture streaming such as massive dataor non-compression HD video. However, since it is difficult for the 60GHz frequency band to pass through an obstacle, it is disadvantageous inthat the 60 GHz frequency band can be used only among devices in ashort-distance space.

Meanwhile, in recent years, as next-generation wireless communicationtechnology standards after the 802.11ac and 802.11ad, discussion forproviding a high-efficiency and high-performance wireless communicationtechnology in a high-density environment is continuously performed. Thatis, in a next-generation wireless communication technology environment,communication having high frequency efficiency needs to be providedindoors/outdoors under the presence of high-density terminals and baseterminals and various technologies for implementing the communicationare required.

Especially, as the number of devices using a wireless communicationtechnology increases, it is necessary to efficiently use a predeterminedchannel. Therefore, required is a technology capable of efficientlyusing bandwidths by simultaneously transmitting data between a pluralityof terminals and base terminals.

DISCLOSURE Technical Problem

An object of the present invention is to provide a wirelesscommunication method and a wireless communication terminal in ahigh-density environment including an overlapped basic service set.

Technical Solution

According to an embodiment of the present invention, a wirelesscommunication terminal that communicates wirelessly includes: atransceiver; and a processor, wherein the processor is configured toreceive a signaling field of a first PLCP Protocol Data Unit (PPDU)through the transceiver, and access a channel based on informationidentifying a Basic Service Set (BSS) indicated by the signaling field.

When a first determination on whether a BSS including the first PPDU isthe same as a BSS including the wireless communication terminal based onthe information identifying the BSS differs from a second determinationon whether the BSS including the first PPDU is the same as the BSSincluding the wireless communication terminal based on an Address fieldof a MAC header included in the PPDU, the processor may be configured toaccess a channel based on the second determination, wherein the Addressfield of the MAC header may indicate a MAC address related to a MACProtocol Data Unit (MPDU).

A size of a field indicating the information identifying the BSS may besmaller than a maximum number that the MAC address is able to have.

The processor may be configured to determine the BSS including the firstPPDU based on at least one of a transmitting STA address (TA) field, areceiving STA address (RA) field, and a BSSID field of the Address fieldof the MAC header.

When the first PPDU includes a trigger frame transmitted from a BSSdifferent from the BSS including the wireless communication terminal,the processor may be configured to measure a received signal strength ofthe first PPDU, and adjust a transmission power based on the receivedsignal strength when transmitting a second PPDU after the transmissionof the trigger frame is completed.

When transmitting the second PPDU while an uplink PPDU transmitted basedon the trigger frame is transmitted, the processor may be configured toadjust a transmission power based on the received signal strength.

When transmitting the second PPDU during Transmission Opportunity (TXOP)indicated by the trigger frame, the processor may be configured toadjust a transmission power based on the received signal strength.

The signaling field of the first PPDU may include information indicatingwhether a Spatial Reuse (SR) operation is allowed, wherein the processormay be configured to adjust the transmission power based on theinformation indicating whether the SR operation is allowed.

The signaling field of the first PPDU may include information on atransmission power of the first PPDU.

A frequency band used by the wireless communication terminal may bedivided into a primary channel and a secondary channel, and theprocessor may be configured to perform a CCA operation on each of theprimary channel and the secondary channel.

The processor may be configured to use a Clear Channel Assessment (CCA)threshold different from a CCA threshold used in the primary channel, inthe secondary channel.

The processor may determine that if a PPDU is not transmitted in theprimary channel, a PPDU transmitted from the secondary channel istransmitted from a BSS different from the BSS including the wirelesscommunication terminal.

According to an embodiment of the present invention, an operating methodof a wireless communication terminal that communicates wirelesslyincludes: receiving a signaling field of a first PLCP Protocol Data Unit(PPDU); and accessing a channel based on information identifying a BasicService Set (BSS) indicated by the signaling field.

The accessing of the channel may include, when a first determination onwhether a BSS including the first PPDU is the same as a BSS includingthe wireless communication terminal based on the BSS color differs froma second determination on whether the BSS including the first PPDU isthe same as the BSS including the wireless communication terminal basedon an Address field of a MAC header included in the PPDU, accessing achannel based on the second determination, wherein the Address field ofthe MAC header may indicate a MAC address related to a MAC Protocol DataUnit (MPDU).

A size of a field indicating the information identifying the BSS may besmaller than a maximum number that the MAC address is able to have.

The accessing of the channel based on the second determination mayinclude determining the BSS including the first PPDU based on at leastone of a transmitting STA address (TA) field, a receiving STA address(RA) field, and a BSSID field of the Address field of the MAC header.

The first PPDU may include a trigger frame transmitted from a BSSdifferent from the BSS including the wireless communication terminal,and the method may further include measuring a received signal strengthof the first PPDU, and adjusting a transmission power based on thereceived signal strength when transmitting a second PPDU after thetransmission of the trigger frame is completed.

The transmitting of the second PPDU may include, when transmitting thesecond PPDU while an uplink PPDU transmitted based on the trigger frameis transmitted, adjusting a transmission power based on the receivedsignal strength.

The signaling field of the first PPDU may include information indicatingwhether a Spatial Reuse (SR) operation is allowed, and the transmittingof the second PPDU may include adjusting the transmission power based onthe information indicating whether the SR operation is allowed.

The signaling field of the first PPDU may include information on atransmission power of the first PPDU.

Advantageous Effects

An embodiment of the present invention is to provide a wirelesscommunication method and a wireless communication terminal in a denseenvironment including an overlapped basic service set.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a wireless LAN system according to an embodiment of thepresent invention.

FIG. 2 shows a wireless LAN system according to another embodiment ofthe present invention.

FIG. 3 shows a block diagram illustrating a configuration of a stationaccording to an embodiment of the inventive concept.

FIG. 4 shows a block diagram illustrating a configuration of an accesspoint according to an embodiment of the present invention.

FIG. 5 shows a process that a station sets an access point and a linkaccording to an embodiment of the present invention.

FIG. 6 shows the wireless communication terminal according to anembodiment of the present invention accessing a wireless medium througha contention procedure.

FIG. 7 shows a PPDU format used in a wireless communication methodaccording to an embodiment of the present invention.

FIG. 8 shows an A-MPDU format used in a wireless communication methodaccording to an embodiment of the present invention.

FIG. 9 shows an operation of a wireless communication terminal when thewireless communication terminal according to an embodiment of thepresent invention receives a PPDU indicating a BSS color correspondingto a BSS including a wireless communication terminal.

FIG. 10 shows an operation of a wireless communication terminal when thewireless communication terminal according to an embodiment of thepresent invention receives a PPDU indicating a BSS color correspondingto an OBSS.

FIG. 11 shows a case where an inter-BSS color collision or an intra-BSScolor confusion occurs.

FIG. 12 shows an operation of a wireless communication terminal when thewireless communication terminal according to an embodiment of thepresent invention receives a legacy PPDU corresponding to an OBSS.

FIGS. 13 and 14 show SR and power save operations of a wirelesscommunication terminal according to the type of PPDU and whether it isan OBSS when the wireless communication terminal according to theembodiment of the present invention receives the PPDU.

FIG. 15 shows a method of determining whether a frame received by awireless communication terminal according to an embodiment of thepresent invention is an Intra-BSS frame or an Inter-BSS frame.

FIG. 16 shows a method for determining whether a received frame is anIntra-BSS frame or an Inter-BSS frame according to a type of a frame anda value of a MAC header field of a wireless communication terminalaccording to an embodiment of the present invention.

FIG. 17 shows the operation of the wireless communication terminal forcorrecting the Inter-BSS color collision situation and the operation ofthe wireless communication terminal to prevent the Intra-BSS colorconfusion when the wireless communication terminal according to theembodiment of the present invention detects an inter-BSS colorcollision.

FIG. 18 shows a method of bonding a frequency band for a broadbandcommunication according to an embodiment of the present invention.

FIG. 19 shows a method of transmitting a broadband PPDU by a wirelesscommunication terminal according to an embodiment of the presentinvention.

FIG. 20 shows that a wireless communication terminal according to anembodiment of the present invention transmits a PPDU through a frequencyband having a frequency bandwidth of 40 MHz.

FIG. 21 shows that a wireless communication terminal according to anembodiment of the present invention adjusts transmission power in an SRoperation.

FIG. 22 shows that a wireless communication terminal according to anembodiment of the present invention performs an SR operation consideringa transmission probability of a PPDU transmitted in an OBSS.

FIG. 23 shows the operation of a wireless communication terminalaccording to an embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. The presentinvention may, however, be embodied in different forms and should not beconstructed as limited to the embodiments set forth herein. Parts notrelating to description are omitted in the drawings in order to clearlydescribe the present invention and like reference numerals refer to likeelements throughout.

Furthermore, when it is described that one comprises (or includes orhas) some elements, it should be understood that it may comprise (orinclude or has) only those elements, or it may comprise (or include orhave) other elements as well as those elements if there is no specificlimitation.

This application claims priority to and the benefit of Korean PatentApplication Nos. 10-2015-0146203 (2015 Oct. 20), Nos. 10-2015-0150311(2015 Oct. 28), 10-2015-0154100 (2015 Nov. 3), 10-2016-0029975 (2016Mar. 12), 10-2016-0044465 (2016 Apr. 11), and 10-2016-0062425 (2016 May20) filed in the Korean Intellectual Property Office and the embodimentsand mentioned items described in the respective applications areincluded in the Detailed Description of the present application.

FIG. 1 is a diagram illustrating a wireless communication systemaccording to an embodiment of the present invention. For convenience ofdescription, an embodiment of the present invention is described throughthe wireless LAN system. The wireless LAN system includes one or morebasic service sets (BSS) and the BSS represents a set of apparatuseswhich are successfully synchronized with each other to communicate witheach other. In general, the BSS may be classified into an infrastructureBSS and an independent BSS (IBSS) and FIG. 1 illustrates theinfrastructure BSS between them.

As illustrated in FIG. 1, the infrastructure BSS (BSS1 and BSS2)includes one or more stations STA1, STA2, STA3, STA4, and STA5, accesspoints PCP/AP-1 and PCP/AP-2 which are stations providing a distributionservice, and a distribution system (DS) connecting the multiple accesspoints PCP/AP-1 and PCP/AP-2.

The station (STA) is a predetermined device including medium accesscontrol (MAC) following a regulation of an IEEE 802.11 standard and aphysical layer interface for a wireless medium, and includes both anon-access point (non-AP) station and an access point (AP) in a broadsense. Further, in the present specification, a term ‘terminal’ may beused to refer to a concept including a wireless LAN communication devicesuch as non-AP STA, or an AP, or both terms. A station for wirelesscommunication includes a processor and a transceiver and according tothe embodiment, may further include a user interface unit and a displayunit. The processor may generate a frame to be transmitted through awireless network or process a frame received through the wirelessnetwork and besides, perform various processing for controlling thestation. In addition, the transceiver is functionally connected with theprocessor and transmits and receives frames through the wireless networkfor the station.

The access point (AP) is an entity that provides access to thedistribution system (DS) via wireless medium for the station associatedtherewith. In the infrastructure BSS, communication among non-APstations is, in principle, performed via the AP, but when a direct linkis configured, direct communication is enabled even among the non-APstations. Meanwhile, in the present invention, the AP is used as aconcept including a personal BSS coordination point (PCP) and mayinclude concepts including a centralized controller, a base station(BS), a node-B, a base transceiver system (BTS), and a site controllerin a broad sense.

A plurality of infrastructure BSSs may be connected with each otherthrough the distribution system (DS). In this case, a plurality of BSSsconnected through the distribution system is referred to as an extendedservice set (ESS).

FIG. 2 illustrates an independent BSS which is a wireless communicationsystem according to another embodiment of the present invention. Forconvenience of description, another embodiment of the present inventionis described through the wireless LAN system. In the embodiment of FIG.2, duplicative description of parts, which are the same as or correspondto the embodiment of FIG. 1, will be omitted.

Since a BSS3 illustrated in FIG. 2 is the independent BSS and does notinclude the AP, all stations STA6 and STA7 are not connected with theAP. The independent BSS is not permitted to access the distributionsystem and forms a self-contained network. In the independent BSS, therespective stations STA6 and STA7 may be directly connected with eachother.

FIG. 3 is a block diagram illustrating a configuration of a station 100according to an embodiment of the present invention.

As illustrated in FIG. 3, the station 100 according to the embodiment ofthe present invention may include a processor 110, a transceiver 120, auser interface unit 140, a display unit 150, and a memory 160.

First, the transceiver 120 transmits and receives a wireless signal suchas a wireless LAN physical layer frame, or the like and may be embeddedin the station 100 or provided as an exterior. According to theembodiment, the transceiver 120 may include at least one transmit andreceive module using different frequency bands. For example, thetransceiver 120 may include transmit and receive modules havingdifferent frequency bands such as 2.4 GHz, 5 GHz, and 60 GHz. Accordingto an embodiment, the station 100 may include a transmit and receivemodule using a frequency band of 6 GHz or more and a transmit andreceive module using a frequency band of 6 GHz or less. The respectivetransmit and receive modules may perform wireless communication with theAP or an external station according to a wireless LAN standard of afrequency band supported by the corresponding transmit and receivemodule. The transceiver 120 may operate only one transmit and receivemodule at a time or simultaneously operate multiple transmit and receivemodules together according to the performance and requirements of thestation 100. When the station 100 includes a plurality of transmit andreceive modules, each transmit and receive module may be implemented byindependent elements or a plurality of modules may be integrated intoone chip.

Next, the user interface unit 140 includes various types of input/outputmeans provided in the station 100. That is, the user interface unit 140may receive a user input by using various input means and the processor110 may control the station 100 based on the received user input.Further, the user interface unit 140 may perform output based on acommand of the processor 110 by using various output means.

Next, the display unit 150 outputs an image on a display screen. Thedisplay unit 150 may output various display objects such as contentsexecuted by the processor 110 or a user interface based on a controlcommand of the processor 110, and the like. Further, the memory 160stores a control program used in the station 100 and various resultingdata. The control program may include an access program required for thestation 100 to access the AP or the external station.

The processor 110 of the present invention may execute various commandsor programs and process data in the station 100. Further, the processor110 may control the respective units of the station 100 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 110 may execute the program foraccessing the AP stored in the memory 160 and receive a communicationconfiguration message transmitted by the AP. Further, the processor 110may read information on a priority condition of the station 100 includedin the communication configuration message and request the access to theAP based on the information on the priority condition of the station100. The processor 110 of the present invention may represent a maincontrol unit of the station 100 and according to the embodiment, theprocessor 110 may represent a control unit for individually controllingsome component of the station 100, for example, the transceiver 120, andthe like. The processor 110 may be a modulator and/or demodulator whichmodulates wireless signal transmitted to the transceiver 120 anddemodulates wireless signal received from the transceiver 120. Theprocessor 110 controls various operations of wireless signaltransmission/reception of the station 100 according to the embodiment ofthe present invention. A detailed embodiment thereof will be describedbelow.

The station 100 illustrated in FIG. 3 is a block diagram according to anembodiment of the present invention, where separate blocks areillustrated as logically distinguished elements of the device.Accordingly, the elements of the device may be mounted in a single chipor multiple chips depending on design of the device. For example, theprocessor 110 and the transceiver 120 may be implemented while beingintegrated into a single chip or implemented as a separate chip.Further, in the embodiment of the present invention, some components ofthe station 100, for example, the user interface unit 140 and thedisplay unit 150 may be optionally provided in the station 100.

FIG. 4 is a block diagram illustrating a configuration of an AP 200according to an embodiment of the present invention.

As illustrated in FIG. 4, the AP 200 according to the embodiment of thepresent invention may include a processor 210, a transceiver 220, and amemory 260. In FIG. 4, among the components of the AP 200, duplicativedescription of parts which are the same as or correspond to thecomponents of the station 100 of FIG. 2 will be omitted.

Referring to FIG. 4, the AP 200 according to the present inventionincludes the transceiver 220 for operating the BSS in at least onefrequency band. As described in the embodiment of FIG. 3, thetransceiver 220 of the AP 200 may also include a plurality of transmitand receive modules using different frequency bands. That is, the AP 200according to the embodiment of the present invention may include two ormore transmit and receive modules among different frequency bands, forexample, 2.4 GHz, 5 GHz, and 60 GHz together. Preferably, the AP 200 mayinclude a transmit and receive module using a frequency band of 6 GHz ormore and a transmit and receive module using a frequency band of 6 GHzor less. The respective transmit and receive modules may performwireless communication with the station according to a wireless LANstandard of a frequency band supported by the corresponding transmit andreceive module. The transceiver 220 may operate only one transmit andreceive module at a time or simultaneously operate multiple transmit andreceive modules together according to the performance and requirementsof the AP 200.

Next, the memory 260 stores a control program used in the AP 200 andvarious resulting data. The control program may include an accessprogram for managing the access of the station. Further, the processor210 may control the respective units of the AP 200 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 210 may execute the program foraccessing the station stored in the memory 260 and transmitcommunication configuration messages for one or more stations. In thiscase, the communication configuration messages may include informationabout access priority conditions of the respective stations. Further,the processor 210 performs an access configuration according to anaccess request of the station. The processor 210 may be a modulatorand/or demodulator which modulates wireless signal transmitted to thetransceiver 220 and demodulates wireless signal received from thetransceiver 220. The processor 210 controls various operations such asradio signal transmission/reception of the AP 200 according to theembodiment of the present invention. A detailed embodiment thereof willbe described below.

FIG. 5 is a diagram schematically illustrating a process in which a STAsets a link with an AP.

Referring to FIG. 5, the link between the STA 100 and the AP 200 is setthrough three steps of scanning, authentication, and association in abroad way. First, the scanning step is a step in which the STA 100obtains access information of BSS operated by the AP 200. A method forperforming the scanning includes a passive scanning method in which theAP 200 obtains information by using a beacon message (S101) which isperiodically transmitted and an active scanning method in which the STA100 transmits a probe request to the AP (S103) and obtains accessinformation by receiving a probe response from the AP (S105).

The STA 100 that successfully receives wireless access information inthe scanning step performs the authentication step by transmitting anauthentication request (S107 a) and receiving an authentication responsefrom the AP 200 (S107 b). After the authentication step is performed,the STA 100 performs the association step by transmitting an associationrequest (S109 a) and receiving an association response from the AP 200(S109 b).

Meanwhile, an 802.1X based authentication step (S111) and an IP addressobtaining step (S113) through DHCP may be additionally performed. InFIG. 5, the authentication server 300 is a server that processes 802.1Xbased authentication with the STA 100 and may be present in physicalassociation with the AP 200 or present as a separate server.

Due to the spread of mobile devices and the supply of wirelesscommunication, wireless communication terminals are increasinglycommunicating in a dense environment. Particularly, the number of caseswhere a wireless communication terminal communicates in an environmentin which a plurality of BSSs are overlapped is increasing. When multipleBSSs are overlapped, the communication efficiency of the wirelesscommunication terminal may be degraded due to interference with otherwireless communication terminals. In particular, when a frequency bandis used through a contention procedure, a wireless communicationterminal may not obtain even a transmission opportunity due tointerference with other wireless communication terminals. To solve thisproblem, a wireless communication terminal may perform a spatial reuse(SR) operation. Specifically, the SR operation may include an operationof accessing the channel depending on whether the received frame is aframe transmitted from a BSS including a wireless communication terminalor a frame transmitted from another BSS. In a specific embodiment, theoperation of accessing the channel may include a CCA operation and adeferral operation. For example, the wireless communication terminal mayadjust a Clear Channel Assessment (CCA) threshold according to whether aframe received by the wireless communication terminal is a frametransmitted from a BSS including the wireless communication terminal ora frame transmitted from an OBSS. Also, the wireless communicationterminal may adjust the transmission power of the PPDU to be transmittedaccording to the result of the CCA operation in the SR operation. Anembodiment for an SR operation of the wireless communication terminalwill be described with reference to FIGS. 6 to 23.

For convenience of explanation, a BSS including a wireless communicationterminal is referred to as Intra-BSS, and a basic service set overlappedwith Intra-BSS is referred to as an Overlapped Basic Service Set (OBSS).In addition, a frame transmitted in the Intra-BSS is referred to as anIntra-BSS frame, and a frame transmitted in the OBSS is referred to asan OBSS frame or an Inter-BSS frame.

FIG. 6 shows the wireless communication terminal according to anembodiment of the present invention accessing a wireless medium througha contention procedure.

The wireless communication terminal performs a carrier sensing in achannel through which data is to be transmitted before transmittingdata. The wireless communication terminal determines that thecorresponding channel is busy when a wireless signal of a predeterminedstrength or more is detected. When a channel is busy, the wirelesscommunication terminal defers access to that channel. This operation isreferred to as Clear Channel Assessment (CCA). In addition, a criterionfor determining whether a wireless communication terminal senses awireless signal is referred to as a CCA threshold. Specifically, whenthe wireless communication terminal detects a wireless signal having aCCA threshold or less, the wireless communication terminal may determinethat the corresponding channel is idle.

When the channel is idle for a predetermined time period or longer, thewireless communication terminal may perform a contention procedureaccording to a backoff window. At this time, the predetermined timeinterval may be any one of InterFrame Space (IFS) defined in 802.11. Forexample, the predetermined time interval may be one of ArbitrationInterFrame Space (AIFS) and PCF InterFrame Space (PIFS). Specifically,the wireless communication terminal may acquire random value in thecontention window as a backoff counter. At this time, when the idle timeof the corresponding channel continues for a slot time or longer, thewireless communication terminal decreases the value of the backoffcounter. At this time, the slot time may be 9 us. The wirelesscommunication terminal waits until the backoff counter value becomes 0.When the value of the backoff counter becomes 0, the wirelesscommunication terminal accesses the corresponding channel. The timeinterval in which the wireless communication terminal decrease the valueof the backoff counter and waits is referred to as a contention windowinterval.

The wireless communication terminal accesses the channel and thentransmits the data. When a channel access of a wireless communicationterminal collision with a channel access of another wirelesscommunication terminal, the wireless communication terminal acquires anrandom number again in the contention window and performs the contentionprocedure. At this time, the wireless communication terminal may adjustthe value of the contention window to twice the previous size.

Also, the channel may become busy before the value of the backoffcounter becomes 0. When the channel is busy before the value of thebackoff counter reaches 0, in a case where the channel is idle again andidle for more than a certain time interval, the wireless communicationterminal may perform the contention procedure again according to thebackoff window. At this time, the wireless communication terminal mayperform the backoff procedure based on the remaining backoff countervalue in the previous contention procedure.

Through the above-described CCA procedure, the wireless communicationterminal may avoid a collision that occurs when a plurality of wirelesscommunication terminals access the same channel. However, if there aretoo many wireless communication terminals in a narrow range and aplurality of OBSSs exist, a low degree of signal interference maycontinuously occur. Therefore, it may be inefficient to perform the sameCCA operation and the deferral operation without distinguishing whetherthe signal is transmitted from the OBSS or the BSS. Therefore, thewireless communication terminal needs to efficiently use the wirelessresources through the SR operation. Specifically, the wirelesscommunication terminal needs to perform CCA and deferral operationsaccording to whether the received frame is an Inter-BSS frame or anIntra-BSS frame. To this end, when the wireless communication terminaltransmits a frame, a method of signaling the BSS including the wirelesscommunication terminal is required. This will be described withreference to FIGS. 7 and 8.

FIG. 7 shows a PPDU format used in a wireless communication methodaccording to an embodiment of the present invention.

FIG. 7(a) shows a PLCP Protocol Data Unit (PPDU) format according to the802.11a/11g standard. Also, FIG. 7(b) shows the PPDU format according tothe 802.11n standard. FIG. 7(c) shows the PPDU format according to the802.11ac standard. FIGS. 7(d) and 7(e) show a PPDU format according toan embodiment of the present invention. FIG. 7(d) shows a case where thePPDU is transmitted through a frequency band having a bandwidth of 20MHz, and FIG. 7(e) shows a case where the PPDU is transmitted through afrequency band having a 40 MHz bandwidth.

A PPDU according to an exemplary embodiment of the present invention isdivided into an L-STF, an L-LTF, an L-SIG field, an RL-SIG field, anHE-SIG-A field, an HE-SIG-B field, an HE-STF, an HE-LTF, an SVC field, adata field, and a Tail & Padding (T&P) field. The wireless communicationterminal performs the OFDM transmission for the L-STF, the L-LTF, theL-SIG field, the RL-SIG field, the HE-SIG-A field, and the HE-SIG-Bfield based on 64 FFT. Also, the wireless communication terminalperforms the OFDM transmission for the HE-STF, the HE-LTF, the SVCfield, the data field, and the Tail&Padding (T&P) field based on 256FFT.

The L-SIG field signals information that may be decoded by a legacywireless communication terminal that does not support embodiments of thepresent invention. L-STF and L-LTF are training signals used for L-SIGfield reception. The legacy wireless communication terminal performsAutomatic Gain Control (AGC) and Frequency Offset Detection (FOD) basedon L-STF and L-LTF. The RL-SIG field signals the PPDU according to anembodiment of the present invention in a form in which the L-SIG fieldis repeated. The HE-SIG-A and HE-SIG-B fields signal information on thePPDU. HE-STF and HE-LTF are training signals for data field reception.The wireless communication terminal may estimate the channel throughwhich the PPDU is transmitted based on the HE-STF and the HE-LTF, andmay perform AGC and FOD. Also, the HE-LTF may be transmitted in avariable number according to the number of spatial streams. HE-LTF maybe divided into HE-LTF-short and HE-LTF-long depending on theapplication. HE-LTF-short is used in communication in indoor environmentand has a duration equivalent to the sum of 6.4 us and a guard interval,and HE-LTF-long is used for communication in outdoor environment and hasa duration equivalent to the sum of 12.8 us and a guard interval.

The data field indicates data included in the PPDU. At this time, thedata may be A-MPDU. The SVC field indicates the start of the data field.Padding in the Tail & Padding (T&P) field indicates a padding bit whenpadding is required for symbol-by-symbol transmission. In the Tai&Padding (T&P) field, Tail is present when the PPDU is protected by aconvolutional code.

The HE-SIG-A field contains information for decoding the PPDU.Specifically, when the PPDU includes the HE-SIG-B field, the HE-SIG-Afield includes a length of the HE-SIG-B field and information onModulation and Coding Scheme (MCS) of the signal including the HE-SIG-Bfield. In addition, the HE-SIG-A field may include an indicatorindicating whether the transmission of the PPDU corresponds to thedownlink transmission or the uplink transmission. In addition, theHE-SIG-A field may include information for identifying the BSS to whichthe wireless communication terminal that transmitted the PPDU belongs.At this time, the information identifying the BSS may be a BSS color.Specifically, the size of the field indicating the BSS color may besmaller than the maximum number that the BSS identifier (BSSID) mayhave. Since the number of symbols that transmit the HE-SIG-A field isfixed at 2, the size of the field that may be used to represent the BSScolor may be limited. In this case, the BSSID may be the MAC address ofthe access point included in the BSS.

The BSS color may be set through various embodiments. Specifically, thewireless communication terminal may set the BSS color based on the MACaddress of the connected access point. In a specific embodiment, thewireless communication terminal may set the BSS color using the MACaddress of the associated access point and any unidirectional function.According to this embodiment, the access point may omit a separateoperation of signaling the BSS color set to the wireless communicationterminal associated to the access point. However, if the size of thefield indicating the BSS color is smaller than the maximum number thatthe MAC address may have, the different BSSs may be set to the same BSScolor even if the MAC address of the access point is unique.

In another specific embodiment, the access point may arbitrarily set theBSS color. At this time, the access point must separately signal the BSScolor set to the wireless communication terminal associated with theaccess point. Specifically, the access point may signal the BSS colorthrough a separate message to the wireless communication terminalassociated with the access point. Also, the wireless communicationterminal may obtain the value of the BSS color from the PPDU transmittedby the access point. As in the previous embodiments, if the size of thefield indicating the BSS color is smaller than the maximum number thatthe MAC address may have, even if the MAC address of the access point isunique, different BSSs may have the same BSS color value.

If the PPDU including the HE-SIG-B field is for a downlink Multi User(MU), the HE-SIG-B field may signal resource allocation information foreach user. In addition, the HE-SIG-B field may have a variable length.Specifically, the number of symbols transmitting the HE-SIG-B field maybe variable.

As described above, the signaling field of the PPDU may includeinformation for identifying the BSS including the wireless communicationterminal that transmitted the PPDU. Therefore, the wirelesscommunication terminal may identify the BSS to which the wirelesscommunication terminal that transmitted the PPDU through the signalingfield of the PPDU belongs. Specifically, the wireless communicationterminal may determine whether the PPDU received based on the signalingfield of the PPDU is the PPDU transmitted from the BSS to which thewireless communication terminal belongs or the PPDU transmitted from theOBSS. For example, the wireless communication terminal may determinewhether the PPDU received based on the BSS color field of the HE-SIG-Afield is the PPDU transmitted from the BSS to which the wirelesscommunication terminal belongs or the PPD transmitted from the OBSS. Theidentification, by the wireless communication terminal, of the BSSincluding a wireless communication terminal which transmitted the PPDUthrough the MAC header will be described with reference to FIG. 8.

FIG. 8 shows an A-MPDU format used in a wireless communication methodaccording to an embodiment of the present invention.

The A-MPDU is an aggregate of a plurality of MPDUs. The A-MPDU mayinclude up to 64 MPDUs. This is because the number of MDPUs that may berepresented by the bitmap of the compressed block ACK is 64. The A-MPDUincludes a delimiter for dividing a plurality of MPDUs and a pad forpadding. The delimiter includes an End-Of-Frame (EOF) field indicatingwhether the corresponding MPDU is the last MPDU among a plurality ofMPDUs included in the A-MPDU, an MPDU Length field indicating the lengthof the MPDU, a CRC field used to check whether the MPDU contains errors,and a signature field.

The individual MPDU includes a frame body including data transmitted bythe MPDU, a MAC header for signaling information on the MPDU, and an FCSfield used for determining whether the MPDU includes an error. At thistime, the frame body may be a MAC Service Data Unit (MSDU) or an A-MSDU,which is an aggregate of a plurality of MSDUs. In addition, the MACheader may include a plurality of Address fields indicating a MACaddress associated with the MPDU. Specifically, the MAC header mayinclude four Address fields. The plurality of Address fields may includeat least one of a BSSID field indicating a BSSID identifying the BSSfrom which the corresponding MPDU is transmitted, a transmitting STAaddress (TA) field indicating a MAC address of the wirelesscommunication terminal transmitting the MPDU, and a receiving STAaddress (RA) field indicating a MAC address of the wirelesscommunication terminal receiving the MPDU. In this case, the BSSID maybe the MAC address of the access point. When an access point transmitsor receives an MPDU, one of a plurality of Address fields may indicate aMAC address of the access point. In addition, the MAC header may includea BSSID field depending on the type of the frame. Therefore, thewireless communication terminal may determine whether the MPDU receivedbased on the MAC header is an Inter-BSS frame or an Intra-BSS frame.Specifically, the wireless communication terminal may determine whetherthe received MPDU is an Inter-BSS frame or an Intra-BSS frame based onthe Address field of the MAC header. For example, when the RA field andthe TA field of the received MPDU indicate the MAC address of the accesspoint to which the wireless communication terminal is associated, thewireless communication terminal may determine the received MPDU as anIntra-BSS frame.

The wireless communication terminal may perform the SR operation basedon whether the corresponding MPDU is an Inter-BSS frame or an Intra-BSSframe. In addition, the wireless communication terminal may perform apower save operation based on whether the MPDU is an Inter-BSS frame oran Intra-BSS frame. In order to determine whether the MPDU received bythe wireless communication terminal based on the MAC header is anInter-BSS frame, the MPDU must be completely received and the FCS fieldmust be decoded. Therefore, when the wireless communication terminalreceives the PPDU including only one MPDU, it may be difficult toperform the SR operation and the power save operation based on the MACheader. When the wireless communication terminal receives the PPDUincluding the A-MPDU, the wireless communication terminal determineswhether the first MPDU of the A-MPDU is an Inter-BSS frame based on theMAC header, and performs the SR operation and the power save operationduring the transmission duration of the remaining MPDUs according towhether the first MPDU of the A-MPDU is the Inter-BSS frame.

In addition, when the wireless communication terminal determined thatthe MPDU received by the wireless communication terminal is an Intra-BSSframe or an Inter-BSS frame, the determination based on the BSS colorindicated by the signaling field of the PPDU may differ from thedetermination based on the Address field of the MAC header. At thistime, the wireless communication terminal may determine whether the MPDUis an Intra-BSS frame or an Inter-BSS frame according to the Addressfield of the MAC header. Specifically, even if the BSS color indicatedby the signaling field of the PPDU is the same as the BSS colorcorresponding to the BSS including the wireless communication terminal,when the value of the Address field of the MAC header corresponding tothe MAC address of the access point is not the MAC address of the accesspoint to which the wireless communication terminal is associated, thewireless communication terminal may determine the received MPDU as anInter-BSS frame. In addition, even if the BSS color indicated by thesignaling field of the PPDU is different from the BSS colorcorresponding to the BSS including the wireless communication terminal,when the value of the Address field of the MAC header corresponding tothe MAC address of the access point is the MAC address of the accesspoint to which the wireless communication terminal is associated, thewireless communication terminal may determine the received MPDU as anIntra-BSS frame.

When the wireless communication terminal receives a wireless signal, thewireless communication terminal may process the received signal in aphysical layer and a MAC layer. At this time, the interface between thephysical layer and the MAC layer is referred a primitive. In addition,the operation of the physical layer of the wireless communicationterminal may be performed by the PHY Sublayer Management Entity (PLME).In addition, the operation of the MAC layer of the wirelesscommunication terminal may be performed by the MAC Sublayer ManagementEntity (MLME). An operation in which a wireless communication terminalreceives a PPDU transmitted from a BSS including a wirelesscommunication terminal and a PPDU transmitted from an OBSS via aprimitive will be described with reference to FIGS. 9 to 11.

FIG. 9 shows an operation of a wireless communication terminal when thewireless communication terminal according to an embodiment of thepresent invention receives a PPDU indicating a BSS color correspondingto a BSS including a wireless communication terminal.

When the wireless communication terminal receives the preamble of thePPDU, the wireless communication terminal measures the received signalstrength indicator (RSSI) and starts receiving the PPDU. The start ofsignal reception may be reported by the PHY-CCA.indication (BUSY,channel-list) primitive from the physical layer of the wirelesscommunication terminal to the MAC layer. At this time, the channel-listparameter may be used to indicate a channel determined to be busy by theCCA when the wireless communication terminal uses a frequency bandwidthhaving a bandwidth greater than 20 MHz.

Upon receiving the PHY-CCA.indication from the physical layer, thewireless communication terminal receives the symbol for transmitting theL-LTF of the PPDU and receives the L-SIG field. The wirelesscommunication terminal decodes the L-SIG field to determine the lengthof the PPDU. If the parity value of the L-SIG field is invalid, thewireless communication terminal receives thePHYRXEND.indication(FormatViolation) primitive from the physical layer.

When the parity value of the L-SIG field is valid and the CRC and otherfields of the HE-SIG-A field are also valid, the wireless communicationterminal determines that the BSS color indicated by the HE-SIG-A is thesame as the BSS color of the BSS including the wireless communicationterminal. As in the embodiment of FIG. 9, when the BSS color indicatedby the HE-SIG-A field is the same as the BSS color of the BSS includingthe wireless communication terminal, the physical layer of the wirelesscommunication terminal maintains the PHY-CCA.indication primitive in theBUSY state during the duration of the L_LENGTH field included in theL-SIG field.

After receiving the HE-SIG-A field, the wireless communication terminalreceives the HE-SIG-B field and the HE training signal. At this time,the HE training signal may be HE-STF and HE-LTF. Depending on the PPDUtransmission mode, the HE-SIG-B field may not be present. Specifically,when the PPDU is a Downlink (DL) Single User (SU) mode, the HE-SIG-Bfield may not exist.

When the PHY-RXSTART.indication(RXVECTOR) primitive is received from thephysical layer, the MAC layer of the wireless communication terminaldetermines that the reception of the PPDU is started. At this time, thePHY-RXSTART.indication(RXVECTOR) primitive includes the received signalstrength indicator (RSSI) value. However, the PPDU may be filtered outin the physical layer according to various conditions. At this time, theMAC layer of the wireless communication terminal receives thePHY-RXEND.indication(Filtered) primitive from the physical layer.Further, when the reception signal is lost before the end of receptionof the PSDU, the MAC layer of the wireless communication terminalreceives the PHY-RXEND.indication(CarrierLost) primitive from thephysical layer. In this case, the MAC layer of the wirelesscommunication terminal receives the PHY-CCA.indication(IDLE) primitivefrom the physical layer after the end of the corresponding PSDU.

When the physical layer of the wireless communication terminalsuccessfully receives the PPDU, the physical layer of the wirelesscommunication terminal combines and decodes the received PSDU bits inunits of octets. The MAC layer of the wireless communication terminalreceives the decoded PSDU from the physical layer via thePHY-DATA.indication(DATA) primitive. The wireless communication terminalmay determine whether it is necessary to receive the MPDU based on theAddress field of the MAC header.

When it is not necessary to receive the MPDU, the wireless communicationterminal stops receiving the PPDU. When the wireless communicationterminal does not need to receive the corresponding MPDU, it may be atleast one of a case where the receiver address of the Address field ofthe corresponding MPDU is different from the MAC address of the wirelesscommunication terminal, or a case where the corresponding MPDU is not abroadcast frame. Specifically, the MAC layer of the wirelesscommunication terminal may stop the PPDU reception by transmitting theMAC-RXEND.request primitive to the physical layer.

When it is necessary to receive the MPDU, the wireless communicationterminal continuously receives the PPDU. The physical layer of thewireless communication terminal transmits thePHY-RXEND.indication(NoError) primitive to the MAC layer aftercompleting reception of the last bit of the PSDU, padding, and Tail.Thereafter, the physical layer of the wireless communication terminalenters the RX IDLE state.

FIG. 10 shows an operation of a wireless communication terminal when thewireless communication terminal according to an embodiment of thepresent invention receives a PPDU indicating a BSS color correspondingto an OBSS.

The wireless communication terminal may perform the SR operation whenreceiving the Inter-BSS frame as described above. Specifically, thewireless communication terminal may adjust the CCA threshold accordingto whether the frame received by the wireless communication terminal isan Intra-BSS frame or an Inter-BSS frame. Therefore, the wirelesscommunication terminal may adjust the CCA threshold based on the BSScolor indicated by the HE-SIG-A field. Specifically, the wirelesscommunication terminal may decode the HE-SIG-A field as described withreference to FIG. 9. If the BSS color indicated by the HE-SIG-A field isdifferent from the BSS color of the BSS including the wirelesscommunication terminal, the wireless communication terminal may performthe CCA by applying the OBSS PD CCA threshold, which is the CCAthreshold used for Preamble Detection (PD) of the PPDU transmitted fromthe OBSS. As in the embodiment of FIG. 10, when the strength of thereceived signal is smaller than the OBSS PD CCA threshold, the wirelesscommunication terminal determines that the corresponding channel isidle. At this time, the physical layer of the wireless communicationterminal may transmit the PHY-CCA.indication (OBSS, IDLE) primitive tothe MAC layer. At this time, the physical layer of the wirelesscommunication terminal may transmit the PHY-CCA.indication (OBSS, IDLE)primitive to the MAC layer. The wireless communication terminal mayperform the CCA by applying the PD CCA threshold, which is the CCAthreshold used for the PPDU PD transmitted from the BSS including thewireless communication terminal, from the time point when transmissionof the PPDU transmitted from the OBSS is terminated. At this time, theOBSS PD CCA threshold may be larger than the PD CCA threshold.

According to the embodiment described with reference to FIG. 10, whenanother wireless communication terminal included in the same BSSdetermines that the BSS color indicated by the signaling field of thePPDU is a BSS color corresponding to the OBSS for some reason, thewireless communication terminal may not receive PPDUs transmitted byother wireless communication terminals included in the same BSS.Further, when the wireless communication terminal inaccuratelydetermines the BSS color corresponding to the BSS including the wirelesscommunication terminal, the wireless communication terminal may notreceive PPDUs transmitted by other wireless communication terminalsincluded in the same BSS. For convenience of explanation, the phenomenonthat the wireless communication terminal does not receive PPDUstransmitted by other wireless communication terminals included in thesame BSS due to BSS color confusion is referred to as intra-BSS colorconfusion.

As described above, since the size of the field indicating the BSS coloris limited, different BSSs may be set to the same BSS color. In thiscase, the wireless communication terminal may apply the PD CCA thresholdinstead of the OBSS PD CCA threshold when a wireless communicationterminal included in another BSS transmits a PPDU. For convenience ofdescription, a case where different BSSs correspond to the same BSScolor is referred to as Inter-BSS color collisions. Specific examples ofIntra-BSS color confusion and Inter-BSS color collision are described inFIG. 11.

FIG. 11 shows a case where an inter-BSS color collision or an intra-BSScolor confusion occurs.

In the embodiment of FIG. 11(a), a first access point HE A, a secondaccess point HE B, and a third access point HE C exist in one space. Atthis time, the second access point HE B and the third access point HE Cmay inadvertently select the same BSS color. At this time, the BSSoperated by the second access point HE B and the BSS operated by thethird access point HE C correspond to the same BSS color, resulting inan inter-BSS color collision.

In the embodiment of FIG. 11(b), the second access point HE B changesthe BSS color to avoid Inter-BSS color collision. The second accesspoint HE B may signal the BSS color change to the wireless communicationterminal included in the BSS operated by the second access point HE B.At this time, if any one of the wireless communication terminalsincluded in the BSS operated by the second access point HE B may notrecognize the BSS color change, Intra-BSS color confusion occurs.

In order to prevent Intra-BSS color confusion and Inter-BSS colorcollisions, the wireless communication terminal may determine whetherthe received MPDU is an Intra-BSS frame or an Inter-BSS frame based onthe Address field of the MAC header as well as the BSS color indicatedby the signaling field of the PPDU. Specifically, when it is determinedthat the MPDU included in the received PPDU is an Intra-BSS frame or anInter-BSS frame, if the determination based on the BSS color indicatedby the HE-SIG-A field is different from the determination based on theAddress field of the MAC header, the wireless communication terminal maydetermine whether the MPDU is an Intra-BSS frame or an Inter-BSS frameaccording to the Address field of the MAC header. This is because theMAC address of the wireless communication terminal is fixed for eachwireless communication terminal and has a unique value, so that it isless likely that the BSS color is duplicated or confused. Therefore, thewireless communication terminal may determine whether intra-BSS colorconfusion and inter-BSS color collision occur based on the MAC header.

Specifically, the wireless communication terminal may determine whetherIntra-BSS color confusion and Inter-BSS color collision occur based onthe Address field of the MAC header. In the specific embodiment, evenwhen Intra-BSS color confusion exists, when the strength of the receivedsignal is greater than the OBSS PD CCA threshold, the wirelesscommunication terminal waits without attempting transmission on thecorresponding channel. At this time, the wireless communication terminalmay check the Address field by decoding the MAC header included in thePPDU. The wireless communication terminal may determine whetherintra-BSS color confusion occurs based on the Address field. Also, whenthe strength of the received signal is smaller than the OBSS PD CCAthreshold, the wireless communication terminal may not attempttransmission immediately after decoding the signaling field of the PPDUand may attempt transmission after decoding the MAC header. Accordingly,the wireless communication terminal may decode the MAC header toidentify the Address field, and determine whether Intra-BSS colorconfusion occurs based on the Address field.

In addition, in a specific embodiment, when the wireless communicationterminal determines whether it is necessary to receive the MPDU based onthe Address field of the MAC header, the wireless communication terminalmay determine whether Intra-BSS color confusion and Inter-BSS colorcollision occur based on the Address field of the MAC header.

FIG. 12 shows an operation of a wireless communication terminal when thewireless communication terminal according to an embodiment of thepresent invention receives a legacy PPDU corresponding to an OBSS.

When the wireless communication terminal receives the legacy PPDU, thewireless communication terminal may perform the SR operation based onthe Address field of the MAC header. This is because the signaling fieldof the legacy PPDU does not include the BSS color. The operation of thewireless communication terminal to receive the L-SIG field of the PPDUmay be the same as the PPDU reception operation described with referenceto FIGS. 9 and 10.

Specifically, when receiving the preamble of the PPDU, the wirelesscommunication terminal measures the received signal strength indicator(RSSI) and starts receiving the PPDU. The start of signal reception maybe reported by the PHY-CCA.indication(BUSY, channel-list) primitive fromthe physical layer of the wireless communication terminal to the MAClayer. At this time, the channel-list parameter may be used to indicatea channel determined to be busy by the CCA when the wirelesscommunication terminal uses with a frequency bandwidth having abandwidth greater than 20 MHz.

Upon receiving the PHY-CCA.indication from the physical layer, thewireless communication terminal receives the symbol for transmitting theL-LTF of the PPDU and receives the L-SIG field. The wirelesscommunication terminal decodes the L-SIG field to determine the lengthof the PPDU. When the parity value of the L-SIG field is invalid, thewireless communication terminal receives thePHYRXEND.indication(FormatViolation) primitive from the physical layer.

When the parity value of the L-SIG field is valid, the wirelesscommunication terminal receives the signaling field after the L-SIGfield.

When the legacy PPDU is a VHT PPDU of the 802.11n standard, the wirelesscommunication terminal receives the VHT-SIG-A field if the parity valueof the L-SIG field is valid. Unlike the HE-SIG-A field, the VHT-SIG-Afield does not contain a BSS color.

After receiving the VHT-SIG-A field, the wireless communication terminalreceives VHT training signals, e.g., VHT-STF and VHT-LTF and VHT-SIG-Bfields. Depending on the specific embodiment, the VHT-SIG-B field maynot be present.

When the MAC layer of the wireless communication terminal receives thePHY-RXSTART.indication(RXVECTOR) primitive from the physical layer, theMAC layer of the wireless communication terminal determines that thereception of the PPDU is started. However, the physical layer of thewireless communication terminal may filter out PPDUs received accordingto various conditions. When the physical layer of the wirelesscommunication terminal filters out the PPDU, the MAC layer of thewireless communication terminal receives thePHY-RXEND.indication(Filtered) primitive from the physical layer.Further, when the reception signal is lost before the end of receptionof the PSDU, the MAC layer of the wireless communication terminalreceives the PHY-RXEND.indication(CarrierLost) primitive from thephysical layer. At this time, the MAC layer of the wirelesscommunication terminal receives the PHY-CCA.indication(IDLE) primitivefrom the physical layer after the end of the corresponding PSDU.

When the wireless communication terminal normally receives the PPDU, thephysical layer of the wireless communication terminal combines anddecodes the received PSDU bits in units of octets. The MAC layer of thewireless communication terminal receives the decoded PSDU from thephysical layer via the PHY-DATA.indication(DATA) primitive. If the PPDUincludes an A-MPDU, the wireless communication terminal may determinewhether the corresponding MPDU is an Intra-BSS frame or an Inter-BSSframe based on the Address field of the MAC header. Specifically, whenthe PPDU includes the A-MPDU, the FCS field of the first MPDU among theplurality of MPDUs included in the A-MPDU may be checked. If the FCSfield is valid, the wireless communication terminal may determinewhether the corresponding MPDU is an Intra-BSS frame or an Inter-BSSframe based on the Address field of the MAC header. In addition, thewireless communication terminal may determine whether it is necessary toreceive the MPDU based on the Address field of the MAC header.

When the wireless communication terminal does not need to receive theMPDU, the wireless communication terminal stops receiving the PPDU. Acase where the wireless communication terminal does not need to receivethe corresponding MPDU may be at least one of a case where thecorresponding MPDU is an Inter-BSS frame as in the embodiment of FIG.12, a case where the receiver address of the address field of the MACheader of the MPDU is different from the MAC address of the wirelesscommunication terminal, and a case where the MPDU is an Intra-BSS framebut not a broadcast frame. Specifically, the MAC layer of the wirelesscommunication terminal may stop the PPDU reception by transmitting theMAC-RXEND.request primitive to the physical layer.

As in the embodiment of FIG. 12, when the corresponding MPDU is anInter-BSS frame, the wireless communication terminal may perform the SRoperation by applying the OBSS PD CCA threshold. Specifically, thewireless communication terminal may perform the CCA by applying the OBSSPD CCA threshold. As in the embodiment of FIG. 12, when the strength ofthe received signal is smaller than the OBSS PD CCA threshold, thewireless communication terminal determines that the correspondingchannel is idle. At this time, the physical layer of the wirelesscommunication terminal may deliver the PHY-CCA.indication(OBSS, IDLE)primitive to the MAC layer, and the MAC layer of the wirelesscommunication terminal may receive the PHY-CCA indication.(OBSS, IDLE)primitive. Also, the wireless communication terminal may perform the CCAby applying the PD CCA threshold from the time point when thetransmission of the PPDU transmitted from the OBSS is terminated.

When the wireless communication terminal needs to receive the MPDU, thewireless communication terminal continuously receives the PPDU. A casewhere the wireless communication terminal needs to receive thecorresponding MPDU may be at least one of a case where the receiveraddress of the Address field of the MAC header of the corresponding MPDUis the same as the MAC address of the wireless communication terminaland a case where the MPDU is an Intra-BSS frame and a broadcast frame.At this time, the MAC layer of the wireless communication terminal doesnot transmit the MAC-RXEND.request primitive to the physical layer. Thephysical layer of the wireless communication terminal transmits thePHY-RXEND.indication(NoError) primitive to the MAC layer aftercompleting reception of the last bit of the PSDU, padding, and Tail.After transmitting the PHY-RXEND.indication(NoError) primitive, thephysical layer of the wireless communication terminal enters the RX IDLEstate.

FIGS. 13 and 14 show SR and power save operations of a wirelesscommunication terminal according to the type of PPDU and whether it isan OBSS when the wireless communication terminal according to theembodiment of the present invention receives the PPDU.

FIG. 13(a) shows SR and power save operations of a wirelesscommunication terminal when the wireless communication terminalaccording to an embodiment of the present invention receives a legacyPPDU.

When the wireless communication terminal receives the legacy PPDU, itmay perform the SR and power save operations based on the MAC header.This is because the signaling field of the legacy PPDU does not containinformation indicating the BSS from which the PPDU was transmitted.Specifically, when the wireless communication terminal receives thelegacy PPDU, the wireless communication terminal may perform the SR andpower save operations based on the Address field of the MAC header. In aspecific embodiment, the wireless communication terminal may perform SRand power save operations based on the Address field of the MAC headerof the first MPDU included in the A-MPDU.

When the first MPDU included in the A-MPDU is an Intra-BSS frame, thewireless communication terminal does not perform the SR operation. Inaddition, when the first MPDU included in the A-MPDU is an Intra-BSSframe, the wireless communication terminal may perform a power saveoperation depending on whether the MPDU is required to be received.Specifically, when the first MPDU included in the A-MPDU is an Intra-BSSframe and the wireless communication terminal does not need to receivethe first MPDU included in the A-MPDU, the wireless communicationterminal may enter the power save mode. Specifically, a case where thewireless communication terminal does not need to receive the first MPDUincluded in the A-MPDU may be at least one of a case where the receiveraddress of the address field of the MAC header of the first MPDUincluded in the A-MPDU is not the MAC address of the wirelesscommunication terminal and a case where the first MPDU included in theA-MPDU is not a broadcast frame.

When the first MPDU included in the A-MPDU is an Inter-BSS frame, thewireless communication terminal may perform the SR operation.Specifically, the wireless communication terminal may perform the CCA byapplying the OBSS PD CCA threshold after the first MPDU included in theA-MPDU. If the first MPDU included in the A-MPDU is an Inter-BSS frame,the wireless communication terminal may not be allowed to enter thepower save mode.

FIGS. 13(b) to 13(d) shows SR and power save operations of a wirelesscommunication terminal when the wireless communication terminalaccording to an embodiment of the present invention receives anon-legacy PPDU. When the wireless communication terminal receives thenon-legacy PPDU, the wireless communication terminal may determinewhether the MPDU included in the PPDU is an Intra-BSS frame or anInter-BSS frame based on the BSS color indicated by the HE-SIG-A fieldof the PPDU. As described above, when the determination based on the BSScolor indicated by the HE-SIG-A field and the determination based on theAddress field of the MAC header are different, the wirelesscommunication terminal may determine whether the MPDU included in thePPDU is an Intra-BSS frame or an Inter-BSS frame according to theAddress field of the MAC header.

FIG. 13(b) shows SR and power save operations of a wirelesscommunication terminal when the wireless communication terminalaccording to an embodiment of the present invention receives an UpLink(UL)/Downlink (DL) SU PPDU.

The wireless communication terminal may first determine whether the MPDUincluded in the PPDU is an Intra-BSS frame or an Inter-BSS frame basedon the BSS color indicated by the HE-SIG-A field. When the BSS colorindicated by the HE-SIG-A field is the same as the BSS color of the BSSincluding the wireless communication terminal, the wirelesscommunication terminal determines the MPDU included in the PPDU as anIntra-BSS frame. When the BSS color indicated by the HE-SIG-A field isdifferent from the BSS color of the BSS including the wirelesscommunication terminal, the wireless communication terminal determinesthe MPDU included in the PPDU as an Inter-BSS frame. At this time, thewireless communication terminal may start the SR operation according tothe determination whether the MPDU included in the PPDU determined basedon the BSS color indicated by the HE-SIG-A field is the Intra-BSS frameor the Inter-BSS frame. In addition, the wireless communication terminalmay start the power save operation according to the determinationwhether the MPDU included in the PPDU determined based on the BSS colorindicated by the HE-SIG-A field is the Intra-BSS frame or the Inter-BSSframe.

However, the wireless communication terminal may determine whether theMPDU is an Intra-BSS frame or an Inter-BSS frame based on the Addressfield of the MAC header of the MPDU. The wireless communication terminalmay change the SR operation according to whether the MPDU determinedbased on the Address field of the MAC header is an Intra-BSS frame or anInter-BSS frame. In addition, the wireless communication terminal maychange the power save operation according to whether the MPDU determinedbased on the Address field of the MAC header is an Intra-BSS frame or anInter-BSS frame. If it is determined that the frame is an intra-BSSframe, the wireless communication terminal may determine whether theaddress of the address field of the MAC header of the MPDU is the sameas the MAC address of the wireless communication terminal. If thereceiver address of the Address field of the MAC header of the MPDU isthe same as the MAC address of the wireless communication terminal, thewireless communication terminal receives the MPDU. When the receiveraddress of the Address field of the MAC header of the MPDU is differentfrom the MAC address of the wireless communication terminal, thewireless communication terminal may enter the power save mode.Specifically, the wireless communication terminal may enter the powersave mode, and may maintain the power save mode until the transmissionof the PPDU is completed. At this time, the wireless communicationterminal may determine whether the PPDU transmission is completed basedon the L_LENGTH field of the L-SIG field. When the wirelesscommunication terminal determines that the MPDU is an Inter-BSS frame,the wireless communication terminal performs the SR operation. Thewireless communication terminal may perform the CCA by applying the OBSSPD CCA threshold. When the strength of the received signal is smallerthan the OBSS PD CCA threshold, the wireless communication terminaldetermines that the corresponding channel is idle. When the wirelesscommunication terminal determines that the MPDU is an Inter-BSS frame,the power save operation of the wireless communication terminal is notpermitted.

FIG. 13(c) shows the SR operation and the power save operation of awireless communication terminal when the wireless communication terminalaccording to the embodiment of the present invention receives a UL MUPPDU.

Since the UL MU PPDU is transmitted through MU-MIMO or OFDMA, it may beinefficient for other wireless communication terminals, except for theaccess point, which is the receiver of the UL MU PPDU, to receive thePSDU included in the UL MU PPDU. Therefore, the wireless communicationterminal receiving the UL MU PPDU may perform the SR operation based onthe BSS color indicated by the HE-SIG-A field without considering theAddress field of the MAC header. In addition, the wireless communicationterminal receiving the UL MU PPDU may perform the power save operationbased on the BSS color indicated by the HE-SIG-A field withoutconsidering the Address field of the MAC header.

When the BSS color indicated by the HE-SIG-A field is the same as theBSS color of the BSS including the wireless communication terminal, thewireless communication terminal may not perform the SR operation. Inaddition, when the BSS color indicated by the HE-SIG-A field and the BSScolor of the BSS including the wireless communication terminal are thesame, the wireless communication terminal may perform the power saveoperation. Specifically, when the BSS color indicated by the HE-SIG-Afield is the same as the BSS color of the BSS including the wirelesscommunication terminal and the wireless communication terminal is notthe access point that is the receiver of the UL MU PPDU, the wirelesscommunication terminal enters the power save mode and maintains thepower save mode until PPDU transmission is completed. At this time, thewireless communication terminal may determine whether the PPDUtransmission is completed based on the L_LENGTH field of the L-SIGfield.

When the BSS color indicated by the HE-SIG-A field is different from theBSS color of the BSS including the wireless communication terminal, thewireless communication terminal may perform the SR operation.Specifically, the wireless communication terminal may perform the CCA byapplying the OBSS PD CCA threshold. When the BSS color indicated by theHE-SIG-A field is different from the color corresponding to the BSSincluding the wireless communication terminal, the wirelesscommunication terminal may not be allowed to enter the power save mode.

FIG. 13(d) shows the SR operation and the power save operation of awireless communication terminal when the wireless communication terminalaccording to the embodiment of the present invention receives the DL MUPPDU.

The user field of the HE-SIG-B field of the DL MU PPDU contains thePartial Association ID (Partial AID) of the wireless communicationterminal receiving the PPDU. Therefore, the wireless communicationterminal may determine whether Intra-BSS color confusion or Inter-BSScolor collision occurs based on the Partial AID of the user field of theHE-SIG-B field. Specifically, the wireless communication terminaldetermines whether the PPDU is an Intra-BSS frame or an Inter-BSS framebased on the BSS color indicated by the HE-SIG-A field, and then, if theuser field of the HE-SIG-B field indicates the Partial AID of thewireless communication terminal, may determine the PPDU as an Intra-BSSframe. In addition, when the BSS color indicated by the HE-SIG-A fieldis the same as the color of the BSS including the wireless communicationterminal and the user field of the HE-SIG-B field does not indicate thePartial AID of the wireless communication terminal, the wirelesscommunication terminal may enter the power save mode. However, only whenthe user field of the HE-SIG-B field indicates the Partial AID of thewireless communication terminal, since Intra-BSS color confusion orInter-BSS color collision may be determined, through the HE-SIG-B field,only intra-BSS color confusion or inter-BSS color collision may bedetermined to be limited. Therefore, even when the wirelesscommunication terminal determines whether Intra-BSS color confusion orInter-BSS color collision occurs based on the Partial AID of the userfield, the wireless communication terminal may again determine intra-BSScolor confusion or inter-BSS color collision based on the Address fieldof the MAC header.

When the wireless communication terminal is an access point, thewireless communication terminal may determine whether Intra-BSS colorconfusion or Inter-BSS color collision occurs through a variety ofmethods than when the wireless communication terminal other than anaccess point. Specifically, when the access point receives the DL SU/MUPPDU indicating the same BSS color as the BSS color of the BSS includingthe access point, the access point may determine that an inter-BSS colorcollision occurs.

Also, when the access point receives a UL SU/MU PPDU that indicates thesame BSS color as the BSS color of the BSS containing the access point,as in the previously described embodiments, when the value of thereceiver address field of the Address field of the MAC header is anaddress other than the MAC address of the access point, the access pointmay determine that an inter-BSS color collision occurs. In addition,when the access point receives the UL SU/MU PPDU indicating the same BSScolor as the BSS color even though the access point does not transmitthe trigger frame, the access point may determine that an inter-BSScolor collision occurs. At this time, the trigger frame is a MAC framefor guiding transmission of the wireless communication terminal.Specifically, the trigger frame may include information on resourcesallocated to the wireless communication terminal by the access point. Ina specific embodiment, the trigger frame may include information on afrequency band allocated to the wireless communication terminal by theaccess point.

Based on an indicator included in the PPDU described above andindicating whether the transmission of the PPDU corresponds to thedownlink transmission or the uplink transmission, the wirelesscommunication terminal may determine whether the received PPDU is an ULPPDU or a DL PPDU.

FIG. 14(a) shows the SR operation and the power save operation of awireless communication terminal depending on whether Inter-BSS colorcollision or Intra-BSS color confusion occurs when the wirelesscommunication terminal according to the embodiment of the presentinvention receives the DL/UL SU PPDU.

When the wireless communication terminal receives the legacy PPDU, thewireless communication terminal may perform the SR operation based onthe Address field of the MAC header. In addition, since the legacy PPDUdoes not include the BSS color, Inter-BSS color collision does notoccur.

When the wireless communication terminal receives the legacy PPDU, thewireless communication terminal may perform the SR operation based onthe Address field of the MAC header. As described above, the wirelesscommunication terminal may determine whether an inter-BSS colorcollision occurs based on the Address field of the MAC header, and maychange the SR operation according to whether an inter-BSS colorcollision occurs. Specifically, when the value of the BSS colorindicated by the signaling field of the PPDU is the same as the BSScolor of the BSS including the wireless communication terminal and it isdetermined based on the Address field of the MAC header that thecorresponding MPDU is an Inter-BSS frame, after receiving the first MPDUincluded in the PPDU, the wireless communication terminal may apply theOBSS PD CCA threshold to perform the CCA. At this time, when thestrength of the received signal is smaller than the OBSS PD CCAthreshold, the wireless communication terminal determines that thecorresponding channel is idle. Accordingly, when the correspondingchannel is idle for a predetermined time or more, the wirelesscommunication terminal may access the corresponding channel. However,when the PPDU includes only one MPDU and it is determined that aninter-BSS color collision occurs based on the MAC header, the wirelesscommunication terminal may not perform the SR operation. There is a highpossibility that there is no MPDU remaining to be received at the timepoint of decoding the MAC header of the MPDU. In addition, when the PPDUincludes only one MPDU, it may include a case where the A-MPDU includesonly one MPDU.

When the value of the BSS color indicated by the signaling field of thePPDU is different from the BSS color of the BSS including the wirelesscommunication terminal and the MPDU is an Intra-BSS frame as a result ofdetermination based on the Address field of the MAC header, the SRoperation may be stopped. When the strength of the received signal issmaller than the OBSS PD CCA threshold and the wireless communicationterminal accesses the corresponding channel, the wireless communicationterminal may stop the transmission on the corresponding channel.

In addition, when the PPDU is transmitted from the BSS including thewireless communication terminal and the wireless communication terminaldoes not need to receive the MPDU included in the PPDU, the wirelesscommunication terminal may perform the power save operation.Specifically, after receiving the first MPDU included in the PPDU, thewireless communication terminal may enter the power save mode. However,if the PPDU includes only one MPDU, the wireless communication terminalmay not perform the power save operation. Also, when the PPDU istransmitted from the OBSS, the power save operation of the wirelesscommunication terminal may not be permitted.

FIG. 14(b) shows the SR operation and the power save operation of awireless communication terminal depending on whether Inter-BSS colorcollision or Intra-BSS color confusion occurs when the wirelesscommunication terminal according to the embodiment of the presentinvention receives the DL/UL MU PPDU.

When the wireless communication terminal receives the non-legacy MU DLPPDU, it may perform a power save operation based on the address of theuser field of the HE-SIG-B field. Specifically, when the BSS colorindicated by the signaling field of the PPDU of the DL MU PPDU is thesame as the BSS color of the BSS including the wireless communicationterminal, and the Partial AID address is not included in the user fieldof the HE-SIG-B field of the DL MU PPDU, the wireless communicationterminal may enter the power save mode. When the wireless communicationterminal receives the non-legacy MU PPDU and the wireless communicationterminal is not the receiver, the wireless communication terminal maynot receive the PSDU included in the MU PPDU. Therefore, when thewireless communication terminal receives the non-legacy DL MU PPDU andthe wireless communication terminal is not the receiver, the wirelesscommunication terminal may not determine whether an inter-BSS colorcollision occurs.

Since the UL MU PPDU is transmitted through MU-MIMO or OFDMA, it may beinefficient for other wireless communication terminals, except for theaccess point, which is the receiver of the UL MU PPDU, to receive thePSDU included in the UL MU PPDU. Therefore, the wireless communicationterminal receiving the UL MU PPDU may perform the SR operation and thepower save operation based on the BSS color indicated by the HE-SIG-Afield without considering the Address field of the MAC header.Specifically, when the BSS color indicated by the signaling field of thePPDU is the same as the BSS color of the BSS including the wirelesscommunication terminal and the wireless communication terminal is notthe access point that is the receiver of the UL MU PPDU, the wirelesscommunication terminal enters the power save mode and maintains thepower save mode until PPDU transmission is completed. At this time, thewireless communication terminal may determine whether the PPDUtransmission is completed based on the L_LENGTH field of the L-SIGfield.

As described above, when the wireless communication terminal receivesthe legacy PPDU transmitted to the MU-MIMO, it may be inefficient forthe wireless communication terminal to receive the PSDU included in thePPDU. Therefore, when the wireless communication terminal receives thelegacy PPDU transmitted to the MU-MIMO, the wireless communicationterminal may not perform the SR operation. In addition, when thewireless communication terminal receives the legacy PPDU transmitted bythe MU-MIMO, the wireless communication terminal may not perform thepower save operation.

The operation of the other wireless communication terminal may be thesame as the case of receiving the DL/UL SU PPDU described above.

It was described through FIGS. 6 to 14 that the wireless communicationterminal according to the embodiment of the present invention performsthe SR operation and the power save operation. In order for the wirelesscommunication terminal according to the embodiment of the presentinvention to perform the SR operation and the power save operation, amethod of determining whether the received frame is an Intra-BSS frameor an Inter-BSS frame has been described. A method for determiningwhether a frame received by a wireless communication terminal is anIntra-BSS frame or an Inter-BSS frame will be described through FIGS. 15and 16.

FIG. 15 shows a method of determining whether a frame received by awireless communication terminal according to an embodiment of thepresent invention is an Intra-BSS frame or an Inter-BSS frame.

As described above, the wireless communication terminal may determinewhether the received frame is an Intra-BSS frame or an Inter-BSS framebased on the BSS color indicated by the signaling field of the PPDU orthe Address field of the MAC header. However, since the size of thefield indicating the BSS color may be limited, different BSSs may havethe same BSS color as described above. In addition, the MAC addressvalue of the wireless communication terminal is unique. Therefore, whenit is determined that the received frame is an Intra-BSS frame or anInter-BSS frame based on the MAC address, the wireless communicationterminal may accurately determine whether the received frame is anIntra-BSS frame or an Inter-BSS frame. Therefore, when the determinationon whether the received frame is an Intra-BSS frame or an Inter-BSSframe based on the BSS color differs from the determination on whetherthe received frame is an Intra-BSS frame or an Inter-BSS frame based onthe Address field of the MAC header, the wireless communication terminalmay determine whether the received frame is an Intra-BSS frame or anInter-BSS frame according to the Address field of the MAC header.Specifically, if the BSS color indicated by the signaling field of thePPDU including the received frame is the same as the BSS color of theBSS including the wireless communication terminal and the Address fieldof the MAC header of the received frame indicates an Inter-BSS frame,the wireless communication terminal may finally determine the receivedframe as an inter-BSS frame. In another specific embodiment, when theBSS color indicated by the signaling field of the PPDU including thereceived frame is different from the BSS color of the BSS including thewireless communication terminal and the Address field of the MAC headerof the received frame indicates an Intra-BSS frame, the wirelesscommunication terminal may finally determine the received frame as anintra-BSS frame.

When any one of the plurality of address fields of the MAC header of theframe received by the wireless communication terminal indicates theBSSID of the BSS including the wireless communication terminal, thewireless communication terminal may determine the received frame as anIntra-BSS frame. In addition, when any one of the plurality of addressfields of the MAC header of the frame received by the wirelesscommunication terminal does not indicate the BSSID of the BSS includingthe wireless communication terminal, the wireless communication terminalmay determine the received frame as an Inter-BSS frame. However,depending on the type of the MAC frame, the wireless communicationterminal may not be able to determine whether the received frame is anIntra-BSS frame or an Inter-BSS frame based on only the Address field.This is because the information indicated by the Address field of theMAC header may vary depending on the setting of the frame type, the ToDS field, and the From DS field. Accordingly, the wireless communicationterminal may determine whether the received frame is an Intra-BSS frameor an Inter-BSS frame based on the type of MAC frame and the MAC Addressfield. This will be described in more detail with reference to FIG. 16.

FIG. 16 shows a method for determining whether a received frame is anIntra-BSS frame or an Inter-BSS frame according to a type of a frame anda value of a MAC header field of a wireless communication terminalaccording to an embodiment of the present invention.

The wireless communication terminal may determine whether the frame is adata frame according to the Type field value of the Frame Control fieldof the MAC header. In the case of a data frame, the informationindicated by the Address field differs depending on the To DS field andthe From DS field. Accordingly, when the Type field of the Frame Controlfield of the MAC header indicates a data frame, the wirelesscommunication terminal may determine whether the received frame is anIntra-BSS frame or an Inter-BSS frame based on the value of the To DSfield, the From DS field and the Address field.

Specifically, if the frame received by the wireless communicationterminal is a data frame and the values of the To DS field and the FromDS field are both 0, the Address 3 field indicates a BSSID. Therefore,when the frame received by the wireless communication terminal is a dataframe and the values of the To DS field and the From DS field are both0, if the value of the Address 3 field is the BSSID of the BSS includingthe wireless communication terminal, the wireless communication terminalmay determine the received frame as an Intra-BSS frame. In addition,when the frame received by the wireless communication terminal is a dataframe and the values of the To DS field and the From DS field are both0, if the value of the Address 3 field is not the BSSID of the BSSincluding the wireless communication terminal, the wirelesscommunication terminal may determine the received frame as an Inter-BSSframe.

In addition, if the frame received by the wireless communicationterminal is a data frame, the To DS field value is 0, and the From DSfield value is 1, the Address 2 field indicates a BSSID. Therefore, whenthe frame received by the wireless communication terminal is a dataframe and the To DS field value is 0 and the From DS field value is 1,if the value of the Address 2 field is the BSSID of the BSS includingthe wireless communication terminal, the wireless communication terminalmay determine the received frame as an Intra-BSS frame. In addition,when the frame received by the wireless communication terminal is a dataframe and the To DS field value is 0 and the From DS field value is 1,if the value of the Address 2 field is not the BSSID of the BSSincluding the wireless communication terminal, the wirelesscommunication terminal may determine the received frame as an Inter-BSSframe. Also, if the To DS field value is 0, the From DS field value is1, and the MSDU included in the MPDU is a basic A-MSDU, the Address 3field indicates a BSSID. Therefore, when the frame received by thewireless communication terminal is a data frame and the To DS fieldvalue is 0 and the From DS field value is 1 and the MSDU included in theMPDU is a basic A-MSDU, if the value of the Address 3 field is the BSSIDof the BSS including the wireless communication terminal, the wirelesscommunication terminal may determine the received frame as an Intra-BSSframe. In addition, when the frame received by the wirelesscommunication terminal is a data frame and the To DS field value is 0and the From DS field value is 1 and the MSDU included in the MPDU is abasic A-MSDU, if the value of the Address 3 field is not the BSSID ofthe BSS including the wireless communication terminal, the wirelesscommunication terminal may determine the received frame as an Inter-BSSframe.

In addition, if the frame received by the wireless communicationterminal is a data frame, the To DS field value is 1, and the From DSfield value is 0, the Address 1 field indicates a BSSID. Therefore, whenthe frame received by the wireless communication terminal is a dataframe and the To DS field value is 1 and the From DS field value is 0,if the value of the Address 1 field is the BSSID of the BSS includingthe wireless communication terminal, the wireless communication terminalmay determine the received frame as an Intra-BSS frame. In addition,when the frame received by the wireless communication terminal is a dataframe and the To DS field value is 1 and the From DS field value is 0,if the value of the Address 1 field is not the BSSID of the BSSincluding the wireless communication terminal, the wirelesscommunication terminal may determine the received frame as an Inter-BSSframe. Also, if the To DS field value is 1, the From DS field value is1, and the MSDU included in the MPDU is a basic A-MSDU, the Address 3field indicates a BSSID. Therefore, when the frame received by thewireless communication terminal is a data frame and the To DS fieldvalue is 1 and the From DS field value is 0 and the MSDU included in theMPDU is a basic A-MSDU, if the value of the Address 3 field is the BSSIDof the BSS including the wireless communication terminal, the wirelesscommunication terminal may determine the received frame as an Intra-BSSframe. In addition, when the frame received by the wirelesscommunication terminal is a data frame and the To DS field value is 1and the From DS field value is 0 and the MSDU included in the MPDU is abasic A-MSDU, if the value of the Address 3 field is not the BSSID ofthe BSS including the wireless communication terminal, the wirelesscommunication terminal may determine the received frame as an Inter-BSSframe. In addition, specifically, when the frame received by thewireless communication terminal is a data frame, the To DS field valueis 1, the From DS field is 1, and the MSDU included in the frame is aBASIC A-MSDU, the Address 3 and Address 4 fields indicate the BSSID.When the frame received by the wireless communication terminal is a dataframe, the To DS field value is 1, the From DS field is 1, and the MSDUincluded in the frame is a BASIC A-MSDU, if the value of the Address 3field or the value of the Address 4 field is the BSSID of the BSSincluding the wireless communication terminal, the wirelesscommunication terminal may determine the received frame as an Intra-BSSframe. In addition, when the frame received by the wirelesscommunication terminal is a data frame, the To DS field value is 1, theFrom DS field is 1, and the MSDU included in the frame is a BASICA-MSDU, if both the value of the Address 3 field and the value of theAddress 4 field are not the BSSID of the BSS including the wirelesscommunication terminal, the wireless communication terminal maydetermine the received frame as an Inter-BSS frame.

When the received frame is a management frame, the Address 1 field is anRA field and the Address 2 field is a TA field. Also, if the receivedframe is a management frame, the Address 3 field may be a BSSID field.Therefore, when the frame received by the wireless communicationterminal is a management frame, if the value of one of the Address 1field, the Address 2 field, and the Address 3 field is the BSSID of theBSS including the wireless communication terminal, the wirelesscommunication terminal may determine the received frame as an Intra-BSSframe. In addition, when the frame received by the wirelesscommunication terminal is a management frame, if all the values of theAddress 1 field, the Address 2 field, and the Address 3 field are notthe BSSID of the BSS including the wireless communication terminal, thewireless communication terminal may determine the received frame as anIntra-BSS frame.

In addition, when the BSS including the wireless communication terminalhas the BSSID included in the multiple BSSID set, when the wirelesscommunication terminal determines that the received frame is anIntra-BSS frame or an Inter-BSS frame, the wireless communicationterminal may regard the BSSID included in the corresponding multipleBSSID set as a BSSID of the BSS including the wireless communicationterminal. Specifically, a case where the value of the address fielddescribed above is the BSSID of the BSS including the wirelesscommunication terminal includes one of a case where the BSS includingthe wireless communication terminal has the BSSID included in themultiple BSSID set and a case where the value of the Address field isany one of a plurality of BSSIDs included in the multiple BSSID set.

Also, a case where the value of the Address field is the BSSID of theBSS including the wireless communication terminal may include a casewhere if the Individual/Group bit is set to 0 in the value of theAddress field, the BSSID of the BSS including the wireless communicationterminal is the same. Also, a case where the value of the Address fieldis the BSSID of the BSS including the wireless communication terminalmay include a case where the value of the Address field is a frequencyband signaling variant of the BSSID of the BSS including the wirelesscommunication terminal.

Also, when the FCS field value of the MPDU is valid, the wirelesscommunication terminal may determine whether the received frame is anIntra-BSS frame or an Inter-BSS frame based on the MAC header or the MACaddress field of the MAC header.

FIG. 17 shows the operation of the wireless communication terminal forcorrecting the Inter-BSS color collision situation and the operation ofthe wireless communication terminal to prevent the Intra-BSS colorconfusion when the wireless communication terminal according to theembodiment of the present invention detects an inter-BSS colorcollision.

When a wireless communication terminal other than an access pointdetects an inter-BSS color collision, the wireless communicationterminal may transmit a frame requesting the BSS color change to theaccess point.

Also, when the access point changes the BSS color, the access point maytransmit a frame indicating a BSS color change. At this time, thewireless communication terminal receiving the frame indicating the BSScolor change may not perform the SR operation based on the BSS colorindicated by the signaling field of the PPDU for a predetermined time.In addition, the wireless communication terminal receiving the frameindicating the BSS color change may not perform the power save operationbased on the BSS color indicated by the signaling field of the PPDU fora predetermined time. At this time, the frame indicating the BSS colorchange may include information indicating a predetermined time. In aspecific embodiment, when a wireless communication terminal having a BSScolor of 1 receives a frame indicating that the BSS color is changed to2, the wireless communication terminal may operate as follows. Thewireless communication terminal may not perform the SR operation for thePPDU indicating the BSS color 2 for a predetermined time from the timepoint when the frame indicating the BSS color change is received. Inaddition, the wireless communication terminal may not perform the powersave operation for the PPDU indicating the BSS color 2 for apredetermined time from the time point when the frame indicating the BSScolor change is received.

In addition, the frame indicating the BSS color change may include acounter indicating the BSS color change history. Specifically, the valueof the counter may be toggled between 0 and 1. In yet another specificembodiment, the value of the counter may increase in a wrap around formwithin a predetermined size range. When the counter value is changed,the wireless communication terminal receiving the frame indicating theBSS color change may determine that the BSS color is changed.

In another specific embodiment, the frame indicating the change in BSScolor may include a counter indicating when the BSS color is applied.Specifically, the access point may periodically transmit a frameindicating a change in the BSS color for a predetermined period of time.In this case, the wireless communication terminal may reduce the countervalue every time the frame indicating the change of the BSS color istransmitted. The wireless communication terminal receiving the frameindicating the change of the BSS color may apply the changed BSS colorwhen the counter value reaches 0.

The wireless communication terminal may prevent Intra-BSS colorconfusion through these operations. A specific embodiment to which suchan operation is applied will be described with reference to FIGS. 17(a)and 17(b).

The embodiment of FIG. 17(a) is a case where a station detects Inter-BSScolor collision. At this time, the station transmits a frame requestingthe BSS color change to the access point. The access point receives theframe requesting the BSS color change and transmits an ACK frame for theframe requesting the BSS color change to the station. The access pointchanges the BSS color and transmits a frame indicating the BSS colorchange. At this time, the counter value of the frame indicating the BSScolor change is 1. The counter value indicates the change history of theBSS color. In addition, the wireless communication terminal receivingthe frame indicating the BSS color change does not perform the SRoperation and the power save operation for a predetermined time fromwhen the frame indicating the BSS color change is received.

The embodiment of FIG. 17(b) is a case where the access point detectsInter-BSS color collision. At this time, the access point transmits aframe indicating BSS color change. Specifically, the access pointperiodically transmits a frame indicating a BSS color change for apredetermined period of time. At this time, the access point indicatesthe BSS color application time by decreasing the counter value includedin the frame indicating the BSS color change. When the wirelesscommunication terminal receives a frame indicating a BSS color changewhose counter value is 0, it applies the changed BSS color.

FIG. 18 shows a method of bonding a frequency band for a broadbandcommunication according to an embodiment of the present invention.

Unless the sub-frequency band is used in the OFDMA transmission, thewireless communication terminal may use a frequency band having afrequency bandwidth of 20 MHz, 40 MHz, 80 MHz, and 160 MHz.Specifically, the wireless communication terminal may bond and use aprimary channel having a frequency bandwidth of 20 MHz and a secondarychannel adjacent to the primary channel and having a bandwidth of 20MHz. At this time, the primary channel is designated for each accesspoint. Also, the bonded frequency band may be referred to as the primary40 MHz channel. In addition, the wireless communication terminal maybond and use a primary 40 MHz channel and a secondary channel having a40 MHz bandwidth and adjacent to the primary 40 MHz channel. At thistime, the bonded frequency band may be referred to as the primary 80 MHzchannel. In addition, the wireless communication terminal may bond anduse a primary 80 MHz channel and a secondary channel having an 80 MHzbandwidth and adjacent to the primary 80 MHz channel. In addition, thewireless communication terminal may bond and use a primary 80 MHzchannel and a secondary channel having an 80 MHz bandwidth and notadjacent to the primary 80 MHz channel. For convenience of description,a frequency band having a frequency bandwidth or 20 MHz or more isreferred to herein as a broadband. When the wireless communicationterminal performs the broadband communication, the bandwidth of thefrequency band required for the CCA also increases. Therefore, when awireless communication terminal accesses a channel through a contentionprocedure, an efficient CCA method for broadband is needed. A method ofthe wireless communication terminal to perform the CCA for the broadbandwill be described with reference to FIGS. 19 and 20.

FIG. 19 shows a method of transmitting a broadband PPDU by a wirelesscommunication terminal according to an embodiment of the presentinvention.

The wireless communication terminal may perform a contention procedurefor a primary channel having a channel-unit frequency bandwidth. At thistime, the wireless communication terminal may transmit a PPDU by bondinga sub-channel which is idle for a preceding predetermined time from atransmission time determined by a contention procedure in a primarychannel. Specifically, the secondary channel may be a frequency bandadjacent to the primary channel. Also, the predetermined time may bePIFS. In addition, the channel-unit frequency bandwidth represents theminimum frequency bandwidth that the wireless communication terminal mayuse when the wireless communication terminal does not use thesub-frequency band in the OFDMA transmission. The channel-unit frequencybandwidth may be 20 MHz as described above.

The specific operation of the wireless communication terminal in thecontention procedure may be the same as the embodiment described withreference to FIG. 6. Specifically, when the channel is idle more than apredetermined time interval, the wireless communication terminal mayperform a contention procedure according to a backoff window. At thistime, the predetermined time interval may be any one of IFS defined in802.11. For example, the predetermined time interval may be either AIFSor PIFS. Specifically, the wireless communication terminal may acquireany value in the contention window as a backoff counter. If the idletime of the corresponding channel continues for a slot time or longer,the wireless communication terminal decreases the value of the backoffcounter. At this time, the slot time may be 9 us. The wirelesscommunication terminal waits until the backoff counter value reaches 0.When the value of the backoff counter reaches 0, the wirelesscommunication terminal accesses the corresponding channel.

Also, the channel may become busy before the value of the backoffcounter reaches 0. In this case, when the channel becomes idle again andis idle over a predetermined time interval, the wireless communicationterminal may perform the contention procedure again according to thebackoff window. At this time, the wireless communication terminal mayperform the backoff procedure based on the remaining backoff countervalue in the previous contention procedure.

In the embodiment of FIG. 19(a), the wireless communication terminalperforms a contention procedure on a primary 20 MHz channel. During thepreceding PIFS from when the value of the backoff counter reaches 0,both the secondary 20 MHz channel and the secondary 40 MHz channelmaintain an idle state. Accordingly, the wireless communication terminaltransmits the PPDU at the time point when the value of the backoffcounter becomes 0 through the frequency band having the bandwidth of 80MHz.

In the embodiment of FIG. 19(b), the wireless communication terminalperforms a contention procedure on a primary 20 MHz channel. During thepreceding PIFS from when the value of the backoff counter becomes 0, thesecondary 20 MHz channel maintains an idle state. During the precedingPIFS from when the value of the backoff counter becomes 0, the secondary40 MHz channel does not maintain an idle state. Therefore, the wirelesscommunication terminal transmits the PPDU through a frequency bandhaving a bandwidth of 40 MHz. In the embodiments of FIGS. 19(a) and19(b), the wireless communication terminal must be able to dynamicallyallocate the PPDU according to the bandwidth of the usable frequencyband. A case where it is difficult to dynamically allocate the PPDUaccording to the bandwidth of the usable frequency band of the wirelesscommunication terminal will be described with reference to FIG. 19(c).

When the wireless communication terminal is unable to transmit in thefrequency band corresponding to the frequency bandwidth selected at thetime of preparation for transmission, even if the primary channel isidle for a time greater than the backoff window indicated by the backoffcounter value, the wireless communication terminal may wait withouttransmission. At this time, the wireless communication terminal may waituntil the wireless communication terminal is able to transmit the PPDUin the frequency band corresponding to the frequency bandwidth selectedat the time of preparation for transmission.

In the embodiment of FIG. 19(c), the wireless communication terminalperforms a contention procedure on a primary 20 MHz channel. During thepreceding PIFS from when the value of the backoff counter becomes 0, thesecondary 20 MHz channel is idle, but the secondary 40 MHz channel doesnot maintain an idle state. Therefore, the wireless communicationterminal waits until transmission is possible in the frequency bandhaving the 80 MHz bandwidth.

FIG. 20 shows that a wireless communication terminal according to anembodiment of the present invention transmits a PPDU through a frequencyband having a frequency bandwidth of 40 MHz.

As described above, the wireless communication terminal performs the CCAoperation to determine whether the corresponding channel is idle beforestarting the backoff procedure. Also, the wireless communicationterminal performs the CCA operation to determine whether thecorresponding channel is idle during the slot time in the backoffprocedure. At this time, the wireless communication terminal may performthe CCA operation based on at least one of preamble detection (PD) andenergy detection (ED). Also, the wireless communication terminal mayperform the CCA operation based on Repetition Detection (RD).

The PD is a method in which the wireless communication terminal detectsrepetitive signal patterns transmitted in the L-STF corresponding to thefirst part of the PPDU and detects the strength of a signal used forPPDU transmission. The Energy Detection (ED) is a method in which awireless communication terminal senses the energy intensity of anarbitrary wireless signal. In addition, the RD is a method in which awireless communication terminal detects a repeated pattern in a signalused for PPDU transmission and detects the strength of a signal used forPPDU transmission. The threshold used when the wireless communicationterminal performs the CCA based on the PD in the primary channel isreferred to as a first PD CCA threshold. Also, the threshold used whenthe wireless communication terminal performs the CCA based on the ED inthe primary channel is referred to as a first ED CCA threshold. Also, athreshold used when the wireless communication terminal performs the CCAbased on the RD in the primary channel is referred to as a first RD CCAthreshold. The first RD CCA threshold may be the same as the first PDCCA threshold. When the PPDU received by the wireless communicationterminal is transmitted from the OBSS, the wireless communicationterminal may perform the CCA operation by applying the OBSS first PD CCAthreshold to the PPDUs transmitted through the OBSS. In this case, theOBSS first PD CCA threshold refers to a threshold for performing the CCAbased on the PD in the primary channel. The wireless communicationterminal may determine whether the received PPDU is a PPDU transmittedfrom the OBSS based on at least one of the BSS color indicated by thesignaling field of the PPDU and the Address field of the MAC header.Specifically, the wireless communication terminal may determine whetherthe received PPDU is a PPDU transmitted from the OBSS according to theembodiment described with reference to FIGS. 6 to 16.

In a specific embodiment, the OBSS first PD CCA threshold may be equalto or greater than the first PD CCA threshold and may be less than orequal to the first ED CCA threshold. In addition, the wirelesscommunication terminal may adjust the value of the OBSS first PD basedon the transmission power TXPWR to be used when the wirelesscommunication terminal transmits the PPDU. For example, the wirelesscommunication terminal may adjust the value of the first PD of the OBSSbased on the transmission power TXPWR to be used when the wirelesscommunication terminal transmits the PPDU within the range of the firstPD (−82 dBm)<=OBSS first PD<=first ED (−62 dBm).

As described above, when transmitting a PPDU, the wireless communicationterminal performs the OFDM transmission for a field for a legacywireless communication terminal and a non-legacy signaling field basedon 64 FFT. Specifically, fields for legacy wireless communicationterminals may be L-STF, L-LTF, and L-SIG fields. In addition, thenon-legacy signaling field may also be an RL-SIG field, an HE-SIG-Afield, and an HE-SIG-B field. When the wireless communication terminalOFDM-transmits the PPDU based on 64 FFT, in relation to the signal fortransmitting the PPDU, the data having a duration of 3.2 us and thecyclic prefix (CP) having a duration of 0.4 us or 0.8 us are repeated.Accordingly, the wireless communication terminal may receive about 6 to7 symbols through the CCA during PIFS (25 us), and measure the strengthof the signal.

The wireless communication terminal performs the OFDM transmission forthe data included in the PPDU and a part of the preamble based on 256FFT. When the wireless communication terminal performs the OFDMtransmission for the PPDU based on 256 FFT, in relation to the signalfor transmitting the PPDU, the data having a duration of 12.8 us and thecyclic prefix (CP) having a duration of any one of 0.8 us, 1.6 us, and3.2 us are repeated. Therefore, the wireless communication terminal mayreceive up to one to two symbols through the CCA for PIFS (25 us) andmeasure the strength of the signal. Therefore, when the wirelesscommunication terminal receives a signal for performing the OFDMtransmission of the PPDU using 64 FFT and 256 FFT together, it may bedifficult for the wireless communication terminal to determine whetherthe signal received during the PIFS is a signal for transmitting thePPDU. Accordingly, when the wireless communication terminal fails todetermine whether the signal received by the wireless communicationterminal is a signal for transmitting the PPDU, the wirelesscommunication terminal may perform the CCA based on the ED. In addition,when the wireless communication terminal receives a signal forperforming the OFDM transmission of the PPDU using 64 FFT and 256 FFTtogether, the wireless communication terminal may determine whether thereceived signal is a signal for transmitting the PPDU based on the RD aswell as the PD.

In the embodiment of FIG. 20(a), the wireless communication terminalperforms a contention procedure based on a backoff counter in theprimary channel. At this time, the wireless communication terminalperforms the CCA based on the PD and the ED. Also, as the wirelesscommunication terminal performs the CCA based on PD, ED, and RD in asecondary channel, it is determined whether the back-off countermaintains the idle state for the preceding PIFS from the time when thecounter value becomes 0.

In addition, when the wireless communication terminal is idle for apredetermined time from the transmission time determined through thecontention procedure of the primary channel in the secondary channel,the wireless communication terminal may transmit the PPDU by bonding theprimary channel and the secondary channel, and the predetermined timemay be longer than the PIFS. As described above, when the PPDU istransmitted by the OFDM transmission based on the 256 FFT, it may bedifficult for the wireless communication terminal to determine whetherthe wireless signal is the PPDU during the PIFS. At this time, thepredetermined time may be less than or equal to AIFS. When the wirelesscommunication terminal acquires 0 as the backoff counter in thecontention procedure for the primary channel, the wireless communicationterminal determines whether the primary channel is idle during the AIFStime. Therefore, when the wireless communication terminal determinesthat the secondary channel is idle for a time interval larger than AIFS,the idle time interval required to transmit the PPDU in the secondarychannel may be greater than the idle time interval required to transmitthe PPDU in the primary channel.

In another specific embodiment, the predetermined time may be equal toor less than the sum of the time represented by the AIFS and the timerepresented by the backoff counter. Accordingly, the wirelesscommunication terminal may increase the detection accuracy of the PPDUtransmitted through the secondary channel. However, the detectionaccuracy of the PPDU transmitted through the secondary channel may varydepending on the backoff counter value. In the embodiment of FIG. 20(b),the wireless communication terminal performs a contention procedure inthe primary channel as described in the embodiment of FIG. 20(a). Thewireless communication terminal determines whether the secondary channelmaintains an idle state for the preceding xIFS time from the time whenthe backoff counter is 0 in the contention procedure of the primarychannel. At this time, xIFS may indicate a frame interval larger thanPIFS.

In another specific embodiment, when the wireless communication terminaldetermines whether the secondary channel is idle for a predeterminedtime from the transmission time determined through the contentionprocedure in the primary channel, the wireless communication terminalmay adjust the length of a predetermined time according to themodulation method of the received signal. At this time, the modulationmethod may be either OFDM transmission using 64 FFT or OFDM transmissionusing 256 FFT. Specifically, if the received signal is transmitted bythe OFDM transmission based on 64 FFT in the secondary channel, thewireless communication terminal may determine whether the secondarychannel is idle during the preceding first time interval from thetransmission time determined through the contention procedure in theprimary channel. In addition, if the received signal is OFDM-transmittedbased on 256 FFT in the secondary channel, the wireless communicationterminal may determine whether the secondary channel is idle during thepreceding second time interval from the transmission time determinedthrough the contention procedure in the primary channel. At this time,the first time interval may be shorter than the second time interval. Ina specific embodiment, the first time interval is PIFS and the secondtime interval is greater than the time indicated by the PIFS and may beless than the sum of the time indicated by the AIFS and the timeindicated by the backoff counter.

If the sum of the time indicated by the AIFS and the time indicated bythe backoff counter obtained in the contention procedure of the primarychannel is greater than the minimum time for detecting the OFDMtransmitted signal based on 256 FFT and a wireless communicationterminal receives a signal to be transmitted by the OFDM transmissionbased on 256 FFT in a secondary channel, the time that the wirelesscommunication terminal determines whether the secondary channel remainsidle may be xIFS indicating a time greater than the PIFS. If the sum ofthe time indicated by the AIFS and the time indicated by the backoffcounter obtained in the contention procedure of the primary channel isgreater than the minimum time for detecting the signal transmitted bythe OFDM transmission based on 256 FFT and a wireless communicationterminal receives a signal to be transmitted by the OFDM transmissionbased on 64 FFT in a secondary channel, the time for determining whetherthe secondary channel remains idle may be PIFS or xIFS.

If the sum of the time indicated by the AIFS and the time indicated bythe backoff counter obtained in the contention procedure of the primarychannel is less than the minimum time for detecting the signaltransmitted by the OFDM transmission based on 256 FFT, it may bedetermined whether the secondary channel is idle during the PIFS fromthe transmission time determined through the contention procedure in theprimary channel. At this time, when the wireless communication terminalsenses a signal transmitted by the OFDM transmission based on 256 FFT inthe secondary channel, the wireless communication terminal may determinewhether the secondary channel is idle during the PIFS based on the ED.In addition, when the wireless communication terminal senses a signalOFDM-transmitted based on 64 FFT in the secondary channel, the wirelesscommunication terminal may determine whether the secondary channel isidle during the PIFS based on at least one of PD, RD, and ED. This isbecause the probability of detecting an OFDM symbol is high when awireless communication terminal attempts to detect an OFDM symboltransmitted based on 256 FFT in a secondary channel for a relativelyshort period of time.

In the embodiment of FIG. 20(c) and the embodiment of FIG. 20(d), whenthe signal received by the wireless communication terminal performs OFDMtransmission based on 64 FFT, the wireless communication terminaldetermines whether the secondary channel is idle during the precedingPIFS from the time point when the transmission is determined in thecontention procedure of the primary channel. In addition, when thesignal received by the wireless communication terminal is transmitted bythe transmitted by the OFDM transmission based on 256 FFT, the wirelesscommunication terminal determines whether the secondary channel is idleduring the preceding xIFS from the time point when the transmission isdetermined in the contention procedure of the primary channel. At thistime, xIFS indicates a time larger than PIFS.

The wireless communication terminal may apply different PD CCAthresholds depending on whether the signal received in the secondarychannel is transmitted by the OFDM transmission based on 64 FFT ortransmitted by the OFDM transmission based on 256 FFT. For convenienceof description, a threshold used when the wireless communicationterminal performs the CCA based on the PD in the secondary channel isreferred to as a second PD CCA threshold. Specifically, the wirelesscommunication terminal may apply the second PD CCA threshold, which islarger than the wireless signal transmitted by the OFDM transmissionbased on the 64 FFT, on the wireless signal transmitted by the OFDMtransmission based on the 256 FFT. Even if the signal received on thesecondary channel is an OBSS PPDU, the wireless communication terminalmay apply different PD CCA thresholds according to whether the receivedOBSS PPDU is transmitted by the OFDM transmission based on 64 FFT orwhether the received OBSS PPDU is transmitted by the OFDM transmissionbased on 256 FFT. At this time, the threshold applied to the CCAoperation based on the PD for the OBSS PPDU transmitted from thesecondary channel is referred to as the OBSS second PD CCA threshold.Also, the threshold applied when the OBSS PPDU in the secondary channelis transmitted by the OFDM transmission based on the 64 FFT is referredto as the OBSS second legacy PD CCA threshold, and the threshold appliedwhen the OBSS PPDU in the secondary channel is transmitted by the OFDMtransmission based on 256 FFT is referred to as OBSS second non-legacyPD CCA threshold. Also, the CCA operation based on the ED in thesecondary channel is referred to as a second ED CCA threshold.Specifically, the OBSS second PD CCA threshold may be equal to orgreater than the second PD CCA threshold, and may be less than or equalto the second ED CCA threshold. In addition, the wireless communicationterminal may adjust the OBSS second PD CCA threshold based on thetransmission power TXPWR to be used when the wireless communicationterminal transmits the PPDU. In addition, the second RD CCA threshold,which is a threshold used when the wireless communication terminalperforms the CCA based on RD in the secondary channel, may be equal tothe second PD CCA threshold. For this operation, the wirelesscommunication terminal needs to determine whether an OBSS PPDU isreceived in the secondary channel.

The wireless communication terminal may determine whether the signalreceived in the secondary channel is an OBSS PPDU based on thedetermination of the signal received in the primary channelSpecifically, when receiving a PPDU from a primary channel, the wirelesscommunication terminal may apply a determination on a PPDU received froma primary channel Specifically, when the PPDU received by the wirelesscommunication terminal on the primary channel is a PPDU transmitted fromthe OBSS, the wireless communication terminal may perform the CCAoperation by applying the OBSS first PD CCA threshold to the primarychannel and perform the CCA operation by applying the OBSS second PD CCAthreshold to the secondary channel. At this time, the OBSS first PD CCAthreshold and the OBSS second PD CCA threshold may be the same. In theembodiment of FIG. 20(c), the wireless communication terminal determinesthat the PPDU received in the primary channel is the PPDU transmitted inthe OBSS. Accordingly, the wireless communication terminal performs theCCA operation by applying the OBSS first PD CCA threshold in the primarychannel. Also, the wireless communication terminal performs the CCAoperation by applying the OBSS second PD CCA threshold in the secondarychannel.

In addition, when the PPDU is not detected in the primary channel, thewireless communication terminal may determine that the PPDU detected inthe secondary channel is the PPDU transmitted in the OBSS. This isbecause that the wireless communication terminal included in the sameBSS extends the frequency band, including the primary channel asdescribed with reference to FIG. 18. In the embodiment of FIG. 20(d),the wireless communication terminal does not detect PPDU reception inthe primary channel. Accordingly, the wireless communication terminaldetermines that the PPDU received in the secondary channel is an OBSSPPDU. The wireless communication terminal performs the CCA operation byapplying the OBSS second PD CCA threshold in the secondary channel.

In addition, the OBSS second PD CCA threshold may be equal to or greaterthan the second PD CCA threshold, and may be less than or equal to thesecond ED CCA threshold. The wireless communication terminal may adjustthe OBSS second PD CCA threshold based on the transmission power TXPWRof the PPDU to be transmitted by the wireless communication terminal.

Specifically, the wireless communication terminal may adjust the OBSSsecond legacy PD CCA threshold based on the transmission power TXPWR ofthe PPDU to be transmitted by the wireless communication terminal withina range of second legacy PD CCA threshold (−72 dBm)<=OBSS second legacyPD CCA threshold<=second ED CCA (−62 dBm) threshold. When a 64 FFTOFDM-based symbol is detected, it is unclear whether the PPDU includedin the symbol is a legacy PPDU or a non-legacy PPDU. Therefore, in orderto maintain equity with legacy wireless communication terminals, thewireless communication terminal uses a value greater than −72 dBm, whichis the CCA threshold applied when the legacy wireless communicationterminal performs the secondary channel CCA, as the OBSS second legacyPD CCA threshold.

In another specific embodiment, when the wireless communication terminalsenses an OFDM transmitted signal based on 256 FFT in the secondarychannel, the wireless communication terminal may adjust the OBSS secondnon-legacy PD CCA threshold based on the transmission power TXPWR of thePPDU to be transmitted by the wireless communication terminal within arange of second non-legacy PD CCA threshold (−82 dBm)<=OBSS secondnon-legacy PD CCA threshold<=second ED CCA threshold (−62 dBm). If a 256FFT OFDM based symbol is detected, since it is clear that it is anon-legacy PPDU, so that the problem of equity with a legacy wirelesscommunication terminal may not be considered.

Also, the wireless communication terminal may adjust the OBSS secondlegacy PD CCA threshold and the OBSS second non-legacy PD CCA thresholdbased on the OBSS first PD CCA threshold. Specifically, the wirelesscommunication terminal may apply the OBSS first PD CCA threshold to theOBSS second legacy PD CCA threshold and the OBSS second non-legacy PDCCA threshold. In addition, when the first PD CCA threshold of the OBSSis greater than the second legacy PD CCA threshold of the OBSS, thewireless communication terminal may apply the OBSS first PD CCAthreshold to the OBSS second legacy PD CCA threshold. In this case, whenthe OBSS first PD CCA threshold is equal to or smaller than the OBSSsecond legacy PD CCA threshold, the OBSS first PD CCA threshold may notbe applied to the OBSS second legacy PD CCA threshold.

FIG. 21 shows that a wireless communication terminal according to anembodiment of the present invention adjusts transmission power in an SRoperation.

The wireless communication terminal may set the OBSS PD CCA thresholdbased on the transmission power of the PPDU to be transmitted asdescribed above. Specifically, if the transmission power of the PPDU tobe transmitted is low, the wireless communication terminal may increasethe OBSS PD CCA threshold. Also, if the transmission power of the PPDUto be transmitted is high, the wireless communication terminal mayreduce the OBSS PD CCA threshold. This is because when the wirelesscommunication terminal transmits the PPDU with low transmission power,the influence of the wireless communication terminal on the OBSS issmall, and when a wireless communication terminal transmits a PPDU withhigh transmission power, the influence of the wireless communicationterminal on the OBSS is large. When the wireless communication terminaladjusts the transmission power of the PPDU in the SR operation as wellas the CCA threshold, the influence of the SR operation of the wirelesscommunication terminal on the transmission in the OBSS may be reduced orthe efficiency of the SR operation may be increased.

Therefore, the wireless communication terminal may transmit the PPDUwith the unadjusted transmission power for the SR operation while theOBSS PPDU is transmitted, or transmit the PPDU with the adjustedtransmission power for the SR operation. At this time, the unadjustedpower for the SR operation may be a predetermined transmission power. Inyet another specific embodiment, the unadjusted power for SR operationmay be the maximum transmit power that the wireless communicationterminal may output. In addition, the predetermined transmission powermay be designated by the access point. Specifically, when the wirelesscommunication terminal detects the reception of the OBSS PPDU andapplies the OBSS PD CCA threshold, the wireless communication terminalmay transmit the PPDU by adjusting the transmission power based on theOBSS PD CCA threshold. In addition, when the wireless communicationterminal does not detect the reception of the OBSS PPDU, the wirelesscommunication terminal may transmit the PPDU with the transmission powercorresponding to the PD CCA threshold. Specifically, when the wirelesscommunication terminal does not detect the reception of the OBSS PPDU,the wireless communication terminal may transmit the PPDU withoutadjusting the transmission power according to the PD CCA threshold. Thisis because the PD CCA threshold is not a relatively high CCA thresholdlike the OBSS PD CCA threshold.

In FIG. 21(a), (a)-1 shows a case where the wireless communicationterminal does not receive the PPDU. At this time, the wirelesscommunication terminal performs the CCA operation by applying the firstPD CCA threshold PD1. In addition, the wireless communication terminaltransmits PPDUs with unadjusted transmission power for the SR operation.FIG. 21(a)-2 shows a case where the wireless communication terminalreceives the PPDU in the primary channel and detects that it is the PPDUtransmitted in the OBSS. After the wireless communication terminaldetects the PPDU transmitted from the OBSS in the primary channel, theCCA is performed by applying the OBSS first PD CCA threshold PD1. Thewireless communication terminal determines that the primary channel isidle and performs a contention procedure based on the backoff. When thePPDU transmission is determined according to the contention procedure,the wireless communication terminal transmits the PPDU to thetransmission power TXPWR determined based on the OBSS first PD CCAthreshold PD1.

FIG. 21(b) is a network topology the non-legacy access points HE A, HE Band HE C, the non-legacy stations A-1, A-2, B-1 and C-1 and the legacystation Leg coexist. Also, FIG. 21(c) shows the PPDU format includinginformation related to the SR operation. Through FIGS. 21(b) to 21(c),the operation of the wireless communication terminal to adjust thetransmission power will be described in detail.

A wireless communication terminal other than an access point must applya transmission power such that an access point of a BSS including awireless communication terminal may stably receive a PPDU. For this, awireless communication terminal other than an access point may adjustthe transmission power according to the following embodiments.Specifically, a wireless communication terminal other than an accesspoint may estimate a channel attenuation of a channel through which aPPDU is transmitted from an access point. A wireless communicationterminal other than an access point may determine the transmission powerof the PPDU to be transmitted based on the estimated channelattenuation. At this time, the wireless communication terminal mayestimate the channel attenuation by measuring the received signalstrength (RSSI) of the PPDU transmitted periodically by the access pointwith an explicit transmission power. Specifically, the explicittransmission power may be a known common transmission power at the BSSin which the corresponding PPDU is transmitted. The explicittransmission power may indicate the transmission power that the wirelesscommunication terminal receiving the PPDU knows when the access pointtransmits the PPDU without signaling separately.

In another specific embodiment, the PPDU transmitted by the access pointmay include information on the transmission power at which the accesspoint transmits the PPDU. At this time, the wireless communicationterminal other than the access point may obtain the information on thetransmission power of the access point transmitting the PPDU from thePPDU transmitted by the access point. A wireless communication terminalother than an access point may estimate a channel attenuation based onthe information on transmission power and RSSI. Therefore, the wirelesscommunication terminal other than the access point may adjust thetransmission power of the PPDU to be transmitted based on the receivedsignal strength of the PPDU transmitted by the access point. Inaddition, the wireless communication terminal other than the accesspoint may adjust the transmission power of the PPDU to be transmittedbased on the information on the received signal strength andtransmission power of the PPDU transmitted by the access point.

The PPDU transmitted by the access point may include SR applicationinformation indicating whether transmission power of the PPDU isadjusted. At this time, when the SR application information indicatesthat the PPDU is not the PPDU of which the transmission power isadjusted, the SR application information may indicate that the PPDU istransmitted with the explicit transmission power. In addition, thewireless communication terminal other than the access point may adjustthe transmission power of the PPDU to be transmitted based on the SRapplication information. The specific operation of the wirelesscommunication terminal related to the SR application information will bedescribed with reference to FIG. 21(c).

A wireless communication terminal that is the furthest from the accesspoint in the BSS including the access point or that transmits the PPDUwith the lowest RSSI is required to adjust the transmission power, sothat the access point may reliably receive the PPDU transmitted by theaccess point. To this end, the access point may adjust the transmissionpower according to the following embodiments. Specifically, the accesspoint may estimate the channel attenuation of the channel through whichthe PPDU is transmitted from the wireless communication terminal otherthan the access point. The access point may adjust the transmissionpower of the PPDU to be transmitted based on the estimated channelattenuation. At this time, the access point may estimate the channelattenuation by measuring the RSSI of the PPDU transmitted periodicallyby the wireless communication terminal other than the access point withan explicit transmission power. Specifically, the explicit transmissionpower may be a known common transmission power at the BSS in which thecorresponding PPDU is transmitted. The explicit transmission power mayindicate the transmission power that the access point receiving the PPDUknows when the wireless communication terminal other than the accesspoint transmits the PPDU without signaling separately.

In another specific embodiment, the PPDU transmitted by the wirelesscommunication terminal other than the access point may includeinformation on the transmission power of the wireless communicationterminal that transmits the corresponding PPDU. At this time, the accesspoint may obtain the information on the transmission power at which thewireless communication terminal other than the access point transmitsthe corresponding PPDU, from the PPDU transmitted by the wirelesscommunication terminal other than the access point. The access point mayestimate the channel attenuation of the channel through which the PPDUis transmitted from the wireless communication terminal other than theaccess point based on the information on the transmission power and theRSSI of the PPDU transmitted by the wireless communication terminalother than the access point. Therefore, the access point may adjust thetransmission power of the PPDU to be transmitted based on theinformation on the transmission power and the RSSI.

The PPDU transmitted by the access point may include SR applicationinformation indicating whether the PPDU is applied with transmissionpower adjustment. At this time, when the SR application informationindicates that the PPDU is not the PPDU to which the transmission poweradjustment is applied, the SR application information may indicate thatthe PPDU is transmitted with the explicit transmission power. Inaddition, the wireless communication terminal other than the accesspoint may adjust the transmission power of the PPDU to be transmittedbased on the SR application information. The specific operation of thewireless communication terminal related to the SR applicationinformation will be described with reference to FIG. 21(c).

The wireless communication terminal may measure the RSSI of a PPDUincluding a broadcast frame received from an access point, and transmitthe RSSI of the PPDU including the broadcast frame to the access point.At this time, the broadcast frame may be a beacon frame. The accesspoint may adjust the transmission power of the PPDU to be transmittedbased on the received signal strength transmitted by the wirelesscommunication terminal other than the access point. Specifically, theaccess point may adjust the transmission power of a PPDU to betransmitted based on the RSSI of a PPDU including a broadcast frametransmitted by a wireless communication terminal other than an accesspoint.

As described above, the signaling field of the PPDU may include SRapplication information indicating whether the SR operation is applied.Specifically, the signaling field of the PPDU may include a TXPWRControl Indication (TCI) indicating whether the corresponding PPDU istransmitted based on the transmission power adjustment. In a specificembodiment, the TCI may be a one-bit field indicating whether thecorresponding PPDU was transmitted based on transmission poweradjustment or whether the corresponding PPDU was not transmitted basedon transmission power adjustment.

The wireless communication terminal may perform the SR operation basedon the SR application information included in the PPDU transmitted fromthe OBSS. Specifically, when the SR application information included inthe PPDU transmitted from the OBSS indicates that the SR operation isapplied, the wireless communication terminal may adjust the OBSS PD CCAthreshold based on the SR application information. For example, if theSR application information included in the PPDU transmitted from theOBSS indicates that the SR operation is applied, the wirelesscommunication terminal may adjust the OBSS PD CCA threshold based on thetransmission power of the PPDU transmitted from the OBSS. In anotherspecific embodiment, when the SR application information included in thePPDU transmitted from the OBSS indicates that the SR operation isapplied, the wireless communication terminal may not transmit the PPDUwhile receiving the OBSS PPDU irrespective of the CCA result. When theSR operation is applied to the PPDU transmitted from the OBSS, it istransmitted after ignoring a certain degree of signal interference.Therefore, when the wireless communication terminal performs theadditional SR operation, the possibility that the wireless communicationterminal included in the OBSS may not receive the OBSS PPDU due to anincrease in signal interference may increase.

Referring to the embodiment of FIG. 21(b), the non-legacy station A-2may perform the SR operation while transmitting the PPDUs transmitted bythe non-legacy station B-1 included in the other BSS. At this time, thenon-legacy station C-1 included in the BSS different from that of thenon-legacy station A-2 may receive the PPDUs transmitted by thenon-legacy station A-2, and obtain the SR application informationincluded in the PPDU. When the SR application information indicates thatthe SR operation is applied, the non-legacy station C-1 may adjust theOBSS PD CCA threshold based on the transmission power of the PPDUtransmitted in the OBSS. In addition, the non-legacy station C-1 may nottransmit the PPDU while receiving the PPDU transmitted by the non-legacystation A-2 regardless of the CCA result.

When any one wireless communication terminal transmits the PPDU throughthe SR operation and a wireless communication terminal receiving thePPDU transmits a PPDU in response to the corresponding PPDU, if the SRoperation is not considered, the transmission of the PPDU may interferewith the transmission of the PPDU transmitted in the OBSS. In theembodiment of FIG. 21(b), the non-legacy access point HE A AP mayperform the SR operation while the non-legacy station B-1 transmits thePPDU. At this time, the non-legacy access point HE A AP may transmit thePPDU including the trigger frame by adjusting the transmission power.The non-legacy stations A-1 and A-2 included in the same BSS as thenon-legacy access point HE A AP may transmit the UL MU PPDU based on thetrigger frame. At this time, when the non-legacy stations A-1 and A-2 donot adjust the transmission power to an appropriate strength, thetransmission of the PPDU of the non-legacy stations A-1 and A-2 mayinterfere with the transmission of the PPDU of the non-legacy stationB-1. Therefore, a wireless communication terminal that needs to receivethe PPDU transmission of the non-legacy station B-1 may not receive thePPDU transmitted by the non-legacy station B-1. Therefore, the wirelesscommunication terminal that transmits the response frame for any framemay operate according to the following embodiments.

When the wireless communication terminal transmits the UL MU PPDU basedon the trigger frame, the wireless communication terminal may transmitthe UL MU PPDU by adjusting the transmission power so that the accesspoint may receive the UL MU PPDU. Specifically, the transmission powerof the UL MU PPDU may be adjusted according to the embodiment in whichthe wireless communication terminal other than the access pointdescribed above adjusts the transmission power. In addition, thewireless communication terminal other than the access point may adjustthe transmission power of the UL MU PPDU based on the frequencybandwidth of the frequency band allocated by the wireless communicationterminal. Specifically, when the first frequency bandwidth is largerthan the second frequency band, the wireless communication terminal mayuse a smaller transmission power when transmitting the UL MU PPDUthrough the second frequency bandwidth than when transmitting the UL MUPPDU through the first frequency bandwidth. This is because if thefrequency bandwidth through which the wireless communication terminaltransmits the PPDU is small, the wireless communication terminal maytransmit it to a far distance at the same transmission power. Forexample, when the transmission power at which the wireless communicationterminal transmits the PPDU to the access point through the frequencyband having the frequency bandwidth of 20 MHz is X, if a wirelesscommunication terminal transmits a PPDU to an access point at thetransmission power X through a frequency band having a frequencybandwidth of 10 MHz, the RSSI of the PPDU received by the access pointmay be unnecessarily high. Therefore, when a wireless communicationterminal transmits a PPDU to an access point through a frequency band of10 MHz, the PPDU may be transmitted to the access point with atransmission power less than the transmission power used when the PPDUis transmitted through a frequency band having a frequency bandwidth of20 MHz.

The PPDU including the trigger frame may include the above SRapplication information. In addition, when the wireless communicationterminal transmits the PPDU after the transmission of the PPDU includingthe trigger frame transmitted from the OBSS is completed, thetransmission power may be adjusted based on the PPDU including thetrigger frame transmitted from the OBSS. In addition, when the wirelesscommunication terminal transmits the PPDU after the transmission of thePPDU including the trigger frame transmitted from the OBSS is completed,the transmission power may be adjusted based on the PPDU including thetrigger frame transmitted from the OBSS. Also, when a wirelesscommunication terminal transmits a PPDU within a TransmissionOpportunity TXOP indicated by a trigger frame transmitted from an OBSS,the wireless communication terminal may adjust the transmission power ofthe PPDU based on the PPDU including the trigger frame transmitted fromthe OBSS. Also, at this time, even when the wireless communicationterminal does not perform the CCA operation by applying the OBSS PD CCAthreshold, the wireless communication terminal may transmit the PPDU byadjusting the transmission power based on the trigger frame transmittedfrom the OBSS. In another specific embodiment, the wirelesscommunication terminal may perform the CCA operation by applying theOBSS PD CCA threshold and transmit the PPDU by adjusting thetransmission power based on the trigger frame. In addition, theadjustment of the transmission power based on the PPDU including thetrigger frame by the wireless communication terminal may be to adjustthe transmission power based on the received signal strength of the PPDUincluding the trigger frame.

FIG. 22 shows that a wireless communication terminal according to anembodiment of the present invention performs an SR operation consideringa transmission probability of a PPDU transmitted in an OBSS.

The wireless communication terminal performs an SR operation based onthe PPDU exchange between the wireless communication terminals OBSS TX,OT initiating the data transmission sequence in the OBSS and thewireless communication terminals OBSS RX, OR participating in the datatransmission sequence. At this time, the wireless communication terminalmay be distinguished into a wireless communication terminal MYBSS TX, MTinitiating a data transmission sequence in a BSS including a wirelesscommunication terminal and a wireless communication terminal MYBSS RX,MR participating in a data transmission sequence. The specificrelationship of MR, MT, OT, and OR may be the same as the networktopology shown in FIG. 22(a).

When the received signal strength of the PPDU transmitted by the OT andthe received signal strength of the PPDU transmitted by the OR are bothlower than the OBSS PD CCA threshold, the MT may transmit the PPDU basedon the SR operation. Specifically, when the received signal strength ofthe PPDU transmitted by the OT and the received signal strength of thePPDU transmitted by the OR are both lower than the OBSS PD CCAthreshold, the MT may transmit PPDU by performing CCA based on the OBSSPD CCA threshold. At this time, the MT may keep the data transmission(MY_DATA) between the MT and the MR longer than the data transmissiontime point in the OBSS and the ACK frame transmission end time point forthe data transmission. This is because the MT may not identify thedistance between the MR and the OT and the distance between the MR andthe OR, so that the influence of the PPDU transmitted from the MR on thereception of the OBSS PPDU may not be known. Specifically, the MT maytransmit data as indicated by the dotted line in the embodiments ofFIGS. 22(b), 22(C), and 22(d).

In another specific embodiment, the MT may transmit a PPDU based on theSR operation when the received signal strength of the PPDU transmittedby the OR is equal to or less than the OBSS PD CCA threshold.Specifically, when the received signal strength of the PPDU transmittedby the OR is equal to or less than the OBSS PD CCA threshold, the MT maytransmit the PPDU by performing the CCA based on the OBSS PD CCAthreshold. At this time, the MT may keep the data transmission (MY_DATA)between the MT and the MR shorter than the data transmission time pointin the OBSS and the ACK frame transmission end time point for the datatransmission. Also, the MR may transmit an ACK frame to the MT after thedata transmission in the OBSS is completed. Specifically, the MT maytransmit data as indicated by the solid line in the embodiments of FIGS.22(b), 22(c) and 22(d). This is because the MT may not determine thedistance between the MT and the OT, the distance between the MR and theOT, and the distance between the MR and the OR, so that the influence ofthe PPDU transmitted from the MT or MR on the reception of the OBSS PPDUmay be known.

When the OT transmits a PPDU including an RTS frame and the OR transmitsa PPDU including a CTS frame based on the RTS frame, all the embodimentsdescribed above may be applied.

When the OT transmits a PPDU including the trigger frame and theplurality of ORs transmit the UL MU PPDU based on the trigger frame, theMT may not receive a PPDU including a trigger frame transmitted by theOT and may receive a UL MU PPDU transmitted by the OR based on thetrigger frame. At this time, the MT may transmit the PPDU based on theSR operation irrespective of the received signal strength of the UL MUPPDU measured by the MT. Specifically, this is because that the MT isfar from the OT so that the MT may not receive the PPDU including thetrigger frame that the OT transmits, the MT may transmit the PPDU basedon the SR operation irrespective of the received signal strength of theUL MU PPDU. At this time, the MT may keep the data transmission(MY_DATA) between the MT and the MR shorter than the data transmissiontime point in the OBSS and the ACK frame transmission end time point forthe data transmission. Also, the MR may transmit an ACK frame to the MTafter the data transmission in the OBSS is completed. Since the MT maynot determine the distance between the MT and the OR, MT may bedifficult to determine the influence that the PPDU transmission of theMT will have when the PPDU including the OT's ACK frame is received bythe OR.

When the OT transmits a PPDU including an MU-RTS frame and a pluralityof ORs transmit a PPDU including a Simultaneous CTS (SCTS) based on anMU-RTS frame, the received signal strength of the PPDU including theSCTS frame measured by the wireless communication terminal may be avalue obtained by combining the received signal strengths of PPDUstransmitted by a plurality of ORs. Accordingly, the MT scales thereceived signal strength of the PPDU including the SCTS frame, andperforms the SR operation based on the scaled received signal strength.Specifically, the MT scales the received signal strength of the PPDUincluding the SCTS frame and adjusts the OBSS PD CCA threshold based onthe scaled received signal strength. At this time, the MT may scale thereceived signal strength based on the number of receiving wirelesscommunication terminals represented by the MU-RTS frame. In anotherspecific embodiment, the received signal strength may be scaled based ona pre-specified value.

The wireless communication terminal receives the PPDU transmitted fromthe OBSS and performs the SR operation by applying the OBSS PD CCAthreshold to the corresponding PPDU, or performs the SR operation byapplying the OBSS PD CCA threshold when receiving one of the PPDUstransmitted from the OBSS and receiving the next PPDU transmitted fromthe OBSS. Specifically, when the wireless communication terminalreceives the PPDU including the control frame, the wirelesscommunication terminal may perform the SR operation as in the followingembodiments. When the wireless communication terminal receives the PPDUtransmitted from the OBSS and including only the control frame, thewireless communication terminal may store only the received signalstrength of the corresponding PPDU without performing the SR operationon the PPDU. At this time, when the wireless communication terminalreceives the PPDU including only the control frame transmitted from theOBSS and then receives the PPDU including the data frame transmittedfrom the OBSS, the wireless communication terminal may perform the SRoperation based on the previously stored received signal strength. Whenthe wireless communication terminal receives the PPDU including thecontrol MPDU and the data MPDU or the management MPDU togethertransmitted from the OBSS, when the duration of the PPDU is longer thana predetermined length, the SR operation may be performed when thecorresponding PPDU is received. At this time, the wireless communicationterminal may determine the duration of the PPDU based on the L_LENGTHfield of the L-SIG field.

In addition, when the wireless communication terminal receives the PPDUincluding the data frame, the wireless communication terminal mayperform the SR operation as in the following embodiments. Specifically,when the wireless communication terminal receives a PPDU including oneor more data MPDUs and the duration of the PPDU is less than apredetermined length, the wireless communication terminal may store onlythe received signal strength of the PPDU without performing the SRoperation on the PPDU. Further, after the wireless communicationterminal receives the PPDU including the data frame, when receiving aPPDU including a control frame, the wireless communication terminal maystore only the received signal strength of the corresponding PPDUwithout performing the SR operation for the PPDU. At this time, thecontrol frame may be an ACK frame. The reason that the wirelesscommunication terminal included in the OBSS transmits a data frame andreceives a control frame such as an ACK frame may be an operation fornotifying the surrounding BSSs of the strength of the received signal atthe beginning of the transmission sequence.

In addition, the PPDU may include information indicating that the SRoperation is not allowed. The PPDU including the frame of thetransmitted control frame before the data frame transmission may includeinformation indicating that the SR operation is not permitted. Also, thewireless communication terminal may perform the SR operation based onthe information indicating that the SR operation included in the PPDUtransmitted from the OBSS is not permitted. Specifically, the wirelesscommunication terminal receiving the PPDU including the informationindicating that the SR operation is not permitted may save only thereceived signal strength without performing the SR operation for thePPDU. Also, the SR application information described above may indicatethat the SR operation is not allowed.

FIG. 23 shows the operation of a wireless communication terminalaccording to an embodiment of the present invention.

The wireless communication terminal receives the signaling field of thePPDU (S2301). Specifically, when the wireless communication terminaldetects the transmission of the PPDU, the wireless communicationterminal may start receiving the PPDU and receive the signaling field ofthe PPDU. The wireless communication terminal may receive the signalingfield of the PPDU according to the embodiments described with referenceto FIGS. 9, 10, 12, and 13.

The wireless communication terminal determines information identifyingthe BSS indicated by the signaling field of the PPDU (S2303). At thistime, the signaling field of the PPDU may be the HE-SIG-A fielddescribed above. In addition, the information identifying the BSS may bethe BSS color described above.

The wireless communication terminal performs the SR operation based onthe information identifying the BSS (S2305). Specifically, the wirelesscommunication terminal may access the channel based on the informationidentifying the BSS. In the specific embodiment, the wirelesscommunication terminal may determine whether the corresponding PPDU isthe PPDU transmitted from the BSS including the wireless communicationterminal based on the BSS color. Also, the wireless communicationterminal may determine whether the corresponding PPDU is the PPDUtransmitted from the BSS including the wireless communication terminal,based on the Address field of the MAC header included in the PPDU.Specifically, the wireless communication terminal may determine whetherthe corresponding PPDU is a PPDU transmitted from the BSS including thewireless communication terminal based on at least one of a transmittingSTA address (TA) field, a receiving STA address (RA) field, and a BSSIDfield of an Address field of a MAC header. When the BSS including thewireless communication terminal has the BSSID included in the multipleBSSID set, when the wireless communication terminal determines whetherthe received frame is an Intra-BSS frame or an Inter-BSS frame, thewireless communication terminal may regard a BSSID included in thecorresponding multiple BSSID set as a BSSID of the BSS including thewireless communication terminal. Also, when the wireless communicationterminal determines whether the received frame is an Intra-BSS frame oran Inter-BSS frame, the wireless communication terminal sets theIndividual/Group bit of the Address field of the MAC header to 0, andcompares the value of the Address field with the BSSID of the BSSincluding the wireless communication terminal.

When the first determination on whether the BSS including the PPDU isthe same as the BSS including the wireless communication terminal basedon the information for identifying a BSS indicated by the signalingfield of the PPDU differs from the second determination on whether theBSS including the PPDU is the same as the BSS including the wirelesscommunication terminal based on the Address field of the MAC headerincluded in the PPDU, based on the second determination, the wirelesscommunication terminal may determine whether the BSS including the PPDUis the same as the BSS including the wireless communication terminal.The wireless communication terminal may determine whether thecorresponding PPDU is a PPDU transmitted from the BSS including thewireless communication terminal according to the embodiments describedwith reference to FIGS. 7 and 8 and FIGS. 15 and 16.

The wireless communication terminal may perform the SR operationaccording to whether the PPDU received by the wireless communicationterminal is the PPDU transmitted from the BSS including the wirelesscommunication terminal or the PPDU transmitted from the OBSS.Specifically, the SR operation may include an operation of accessing thechannel depending on whether the received PPDU is a PPDU transmittedfrom a BSS including a wireless communication terminal or a PPDUtransmitted from another BSS. In a specific embodiment, the operation ofaccessing the channel may include a CCA operation and a deferraloperation. For example, the wireless communication terminal may adjust aCCA threshold depending on whether the PPDU received by the wirelesscommunication terminal is a PPDU transmitted from the BSS including thewireless communication terminal or a PPDU transmitted from the OBSS. Atthis time, the wireless communication terminal may perform the CCAoperation based on at least one of PD, ED, and RD. Also, the CCAthreshold may be at least one of a PD CCA threshold, an ED CCAthreshold, and an RD CCA threshold.

Also, when a wireless communication terminal uses a frequency band thatis divided into a primary channel and a secondary channel, the wirelesscommunication terminal may perform the CCA operation in the primarychannel and the secondary channel. Specifically, the wirelesscommunication terminal may use a CCA threshold different from the CCAthreshold used in the primary channel, in the secondary channel. At thistime, the CCA threshold may be the PD CCA threshold. In addition, whenthe PPDU is not transmitted in the primary channel, the wirelesscommunication terminal may determine that the PPDU transmitted in thesecondary channel is transmitted in the BSS different from the BSSincluding the wireless communication terminal. Specifically, when awireless communication terminal uses a frequency band that is dividedinto a primary channel and a secondary channel, the wirelesscommunication terminal may operate according to the embodimentsdescribed with reference to FIGS. 18 to 20.

In addition, in the SR operation, the wireless communication terminalmay adjust the transmission power of the PPDU. The wirelesscommunication terminal may adjust the transmission power based onwhether the wireless communication terminal is an access point or awireless communication terminal other than an access point. In addition,the wireless communication terminal may adjust the transmission power ofthe PPDU to be transmitted based on the type of frame included in thePPDU transmitted from the OBSS. Specifically, the wireless communicationterminal may adjust the transmission power of the PPDU to be transmittedaccording to whether the frame included in the PPDU is a control frameor a data frame. Also, the wireless communication terminal may adjustthe transmission power of the PPDU to be transmitted according towhether the frame included in the PPDU is a trigger frame or an S-CTSframe. In a specific embodiment, when the PPDU received by the wirelesscommunication terminal includes the trigger frame transmitted from theOBSS, the wireless communication terminal may measure the strength ofthe received signal of the PPDU. At this time, after the transmission ofthe trigger frame is completed, the wireless communication terminal maytransmit the PPDU by adjusting the transmission power based on thereceived signal strength. Specifically, the wireless communicationterminal may transmit the PPDU by adjusting the transmission power basedon the received signal strength while the uplink PPDU transmitted basedon the trigger frame is transmitted. In a specific embodiment, thewireless communication terminal may transmit the PPDU by adjusting thetransmit power based on the received signal strength during TransmissionOpportunity (TXOP) indicated by the trigger frame.

In addition, the signaling field of the PPDU may include informationindicating whether the Spatial Reuse (SR) operation is permitted or not,and the transmission power of the PPDU may be adjusted based oninformation indicating whether the SR operation is allowed or not.Specifically, the wireless communication terminal may adjust thetransmission power of the PPDU when the information indicating whetherthe SR operation is permitted indicates an SR operation permission.Specifically, when the information indicating whether the SR operationis permitted indicates that the SR operation is not allowed, thewireless communication terminal may not perform the SR operation for thePPDU. At this time, the wireless communication terminal may store onlythe received signal strength of the corresponding PPDU. In addition, thesignaling field of the PPDU may include information on the transmissionpower of the PPDU. The information on the transmission power may be theTCI field described above. Further, the information on the transmissionpower may be information indicating the transmission power applied tothe transmission of the PPDU. Specifically, the wireless communicationterminal may adjust transmission power according to the embodimentsdescribed with reference to FIGS. 21 and 22.

In addition, the wireless communication terminal may perform the powersave operation according to whether the PPDU received by the wirelesscommunication terminal is a PPDU transmitted from the BSS including thewireless communication terminal or a PPDU transmitted from the OBSS.Specifically, the wireless communication terminal may perform a powersave operation according to the embodiments described with reference toFIG. 9 to FIG. 14.

Although the present invention is described by using wireless LANcommunication as an example, it is not limited thereto and may beapplied to other communication systems such as cellular communication.Additionally, while the method, device, and system of the presentinvention are described in relation to specific embodiments thereof,some or all of the components or operations of the present invention maybe implemented using a computer system having a general purpose hardwarearchitecture.

The features, structures, and effects described in the above embodimentsare included in at least one embodiment of the present invention and arenot necessary limited to one embodiment. Furthermore, features,structures, and effects shown in each embodiment may be combined ormodified in other embodiments by those skilled in the art. Therefore, itshould be interpreted that contents relating to such combination andmodification are included in the range of the present invention.

While the present invention is described mainly based on the aboveembodiments but is not limited thereto, it will be understood by thoseskilled in the art that various changes and modifications are madewithout departing from the spirit and scope of the present invention.For example, each component specifically shown in the embodiments may bemodified and implemented. It should be interpreted that differencesrelating to such modifications and application are included in the scopeof the present invention defined in the appended claims.

The invention claimed is:
 1. A wireless communication terminal thatcommunicates wirelessly, the terminal comprising: a transceiver; and aprocessor, wherein the processor is configured to receive a signalingfield of a Physical Layer Convergence Protocol (PLCP) Protocol Data Unit(PPDU) through the transceiver, obtain an Address field of a MAC headerfrom the PPDU, determine that the PPDU includes an Inter-Basic ServiceSet (BSS) frame when information identifying a BSS indicated by thesignaling field is the same as information identifying a BSS of a BSSincluding the wireless communication terminal, and the obtained Addressfield of the MAC header indicates a BSS which is different from the BSSincluding the wireless communication terminal as a BSS from which thePPDU is transmitted, and access a channel based on the determinationthat the PPDU includes an Inter-BSS frame, wherein the Address field ofthe MAC header indicates a MAC address related to a MAC Protocol DataUnit (MPDU).
 2. The wireless communication terminal of claim 1, whereina maximum number of BSSs being able to be identified by the informationidentifying a BSS is smaller than a maximum number of BSSs being able tobe identified by the MAC address.
 3. The wireless communication terminalof claim 1, wherein the processor is configured to determine whether thePPDU includes an Inter-BSS frame or an Intra-BSS frame based on at leastone of a transmitting STA address (TA) field, a receiving STA address(RA) field, and a BSSID field of the Address field of the MAC header. 4.The wireless communication terminal of claim 1, wherein the processor isconfigured to determine, based on the determination that the PPDUincludes an Inter-BSS frame, a Clear Channel Assessment threshold whichis used for accessing the channel.
 5. The wireless communicationterminal of claim 1, wherein the processor is configured to enter apower save mode based on the determination that the PPDU includes anInter-BSS frame.
 6. An operating method of a wireless communicationterminal that communicates wirelessly, the method comprising: receivinga signaling field of a Physical Layer Convergence Protocol (PLCP)Protocol Data Unit (PPDU) through the transceiver, obtaining an Addressfield of a MAC header from the PPDU, determining that the PPDU includesan Inter-Basic Service Set (BSS) frame when information identifying aBSS indicated by the signaling field is the same as informationidentifying a BSS of a BSS including the wireless communicationterminal, and the obtained Address field of the MAC header indicates aBSS which is different from the BSS including the wireless communicationterminal as a BSS from which the PPDU is transmitted, and accessing achannel based on the determination that the PPDU includes an Inter-BSSframe, wherein the Address field of the MAC header indicates a MACaddress related to a MAC Protocol Data Unit (MPDU).
 7. The operatingmethod of claim 6, wherein a maximum number of BSSs being able to beidentified by the information identifying a BSS is smaller than amaximum number of BSSs being able to be identified by the MAC address.8. The operating method of claim 6, wherein the accessing the channelcomprises determining whether the PPDU includes an Inter-BSS frame or anIntra-BSS frame based on at least one of a transmitting STA address (TA)field, a receiving STA address (RA) field, and a BSSID field of theAddress field of the MAC header.
 9. The operating method of claim 6,wherein the accessing the channel comprises determining a Clear ChannelAssessment threshold which is used for accessing the channel based onthe information identifying a Basic Service Set (BSS) indicated by thesignaling field.